Mandy Milkovich or Amanda Milkovich is the bad girl of Ian's class, shown to be as a true side born of the tracks, Mandy also possesses a sweeter side to her. She is put out as someone not to mess with initially when Ian does not share the same feelings for her, but when she later discovers his sexuality, she agrees to act as his "beard", his fake girlfriend to help keep his sexuality secret. Mandy is noted to be promiscuous and proud of it as she seduces Lip in the second season, before agreeing to do the same to Jody in an attempt to break him and Karen up. Despite acting as Ian's beard, she has no idea that he is in fact having sex with her brother, Mickey.
In the episode Hurricane Monica, it is revealed that Mandy is pregnant. However, in the episode A Great Cause, Mandy tells Ian and Lip that she was impregnated by her father, who sometimes rapes Mandy when drunk. They decide to have a fundraiser to raise money for an abortion. By Just Like the Pilgrims Intended, she had already had an abortion, and was having regular sex with Lip, who was living at her place. Mandy apparently wanted to form a relationship with him, but he was busy thinking about Karen's baby, which turned out not to be his. During Fiona Interrupted, Mandy tells Lip she thinks he should return home to his family, advice which he then follows.
In addition, Mandy possibly has four other brothers other than Mickey. Two of which joined Mickey when Ian was accused of attacking Mandy during Season 1. The other two joined Mickey when he tried to kill Frank in Season 2.
In Season 3 , Mandy is seen living in the Gallagher house, where she almost never wears pants. In The American Dream, she starts to wonder about Lip's IQ. She went to Lip's guidance counselor and asked what he wanted for Lip. She takes an interest in Lip's grades and tries to convince him to apply to college. She also asks Ian what he thought about Lip. At the end of episode 3, she was receiving oral sex from Lip, but when she tried to give Lip fellatio he refused. Earlier in the episode, Lip was conducting a sting against a blonde sex offender, who used Nair on his pubic hair. Mandy notices that Lip is not aroused and that his hair is gone and she realizes he had been with someone else. Lip explains he was gathering evidence against the sex offender as Mandy storms out. Later we see that Mandy had gone to the sex offender's house and threatened she leave. Her brothers are digging a grave in her front lawn, which scares the sex offender who goes back inside to pack her things. The episode ends with her brothers selling the grave site (not wanting to waste it) to be used to a few men with a dead body wrapped in a carpet.
The teaser for episode 4 reveals that Mandy has a half-sister, whom she will visit. At the beginning of the episode, Kevin and Veronica, and at the same time Lip and Mandy are having sex, a call comes in for Mandy and Mandy stops Lip for a moment, but after finding out about her sibling. Lip asks if he should continue and they do. She and Lip decide to go pick her up from a foster home in another state. Mandy does not seem very fond of her half sister to what she refers her to. She does call her a sister when introducing her to everyone minus Carl who is on a camping trip at the time, and everyone gets surprised in finding out she had another sibling. She lives at the Gallagher home at the moment, since Mandy tried to bring her to her aunt but her aunt refuses and tells her to take Molly back. It is revealed that she has a penis when Debbie gave her some clothes to change in and unintentionally made the discovery.
There is a part of her that continues to search for a way out even though, like her brother Mickey, she too believes that she is fucked for life. For a brief period she allows herself to believe that Lip is that way and finds herself going to great lengths to make that happen; including instilling herself in every aspect of his life and trying to be the perfect girlfriend so that Lip does not ever want her to leave. Kevin quotes that she is Ghetto Married. Mandy tries to spend time with Lip while trying to find a new home for Molly. Fiona has started asking Mandy during their brief encounters to help out around the house. She tries to help Lip on Kevin's Ice Cream truck Kevin is delighted and takes up her offer considering he has to head to The Alibi, but Lip refuses her help. Out of frustration, Lip then tells her to go home, creating a small conflict between the two. Mandy goes to her Aunt's home. Ian confronts Lip about the way he is treating Mandy and expresses that he needs to get over Karen and stop treating Mandy like Karen treated him. He calls Karen and leaves an angry message stating various awful things Karen had done in past episodes. Lip finally comes to terms with the fact that he treated Mandy poorly and apologizes to her. She forgives him and Lip blows off some fireworks him and Kevin intend to sell. He and Mandy sit up a blanket and enjoys the fireworks. Mandy and Lip's relationship is now much better.
As it turned out her half sister is a runaway, just like Mandy herself.
Later on, Karen returns and Mandy does not take it well but not enough that it only bothered her that she even spoke with Lip. Mandy tries to sign Lip for college and she needed to steal a few things to do so. Lip, at first, does not take her help well, but eventually, gives her thanks by having sex with her and actually saying thanks. After Lip chooses her over Karen, Karen dislikes his decision and calls Mandy about a few sexual things with Lip. Mandy gets annoyed and insulted and grabs Lip's phone, unbeknownst to him. Karen receives a text from Lip's phone. Karen assumes it to be another chance with Lip. As Karen enters the intersection of the street, a car almost hits her, and Karen puts her middle finger up at the car, only to have Mandy drive her car over Karen, leaving her unconscious on the road. The next day, Mandy is cleaning some blood and broken glass from the car. Mickey asked who she ran over, and Mandy only mentions that it was a girl from school. Mickey then gives her some advice about cleaning up the car. Lip begins to suspect Mandy after a visit to the hospital. Lip refuses to have sex with Mandy, making her upset. Mandy, however, manages to do it in the kitchen after everyone had left for a camping trip. After seeing Karen in her state, Lip decides to go to Mickey's wedding, only to break-up with Mandy, who then reveals she gave a blow job to another guy after Lip's outburst. She is no longer within a relationship with Lip.
Things seem to have calmed down a bit since the break-up. However, she gets a visit from Ian and then Lip. During Ian's visit, however, she knows about Mickey's sexuality. During Lip's visit, Lip thanks her and leaves. She continues to date Kenyatta during Season Four, though it quickly becomes clear that he is violent and abusive if he thinks she is cheating; when Ian sees her with a badly bruised face, he confronts Kenyatta and holds a knife to his throat. She gets work as a waitress at a diner where she encounters Lip and Amanda.
Early in Season Five, Mandy's personality has changed due to her time with Kenyatta; she is much more withdrawn and submissive, not challenging him when he says that they are moving to Indiana despite Ian's angry protests. Ian tells Lip to convince Mandy to stay so that they can get her away from Kenyatta and keep her safe. Lip meets with her and ends up having sex with her, during which she (in tears) says she loves him. Lip says nothing in response, and she leaves for Indiana, miserable.
Mandy returns in Season 6. She reveals having escaped Kenyatta and secretly moved back to Chicago, where she takes a job at an escort agency, that also provides housing for her. However, when she murders a client who tried to strangle her in the heat of the moment, she calls Ian to help her get rid of the corpse. Ian talks her into confessing to the police instead, and as a result, Mandy gets out of the situation without conviction. Ian tries to persuade Mandy into quitting her job, but she assures that, despite the negative aspects and risks of the job, she's able to live more comfortably than she did before and experience better things. As a result, she continues to work for the agency; however, Ian does not judge her, and they remain close friends.
She tenaciously tries to avoid Lip throughout the entire episode. When their ways coincidentally do cross, she flees the situation almost immediately.
Mandy is just as tough, manipulative and promiscuous as Karen, but unlike her is unable to conceal it and does not care to, as she comes from a criminal and abusive home whereas Karen is middle class. She has casual sex with many people and will go to extreme lengths to get revenge if people genuinely wrong her. Like her brothers, this harsh exterior was formed from years of living with their abusive and very dangerous father. She often displayed callous indifference to her "sister's" plight in Season 3, although it later turned out that her opinion was vindicated. Like her brothers, she does not seem to care where she is going in life, nor is she afraid to use extreme violence or coercion; she pulled a shotgun on her father to protect Ian in Season 2 and rammed Karen with a car in Season 3.
Unlike Karen, however; Mandy has a softer side beneath her indifferent exterior -- she is much less selfish than Karen. When she discovers Ian's sexuality, she offers to act as his beard so he can avoid suspicion (although this leads to trouble later on with her father). As her relationship with Lip develops in Season 3, she commits many selfless acts to make Lip's life easier (especially filling out applications to colleges for him when he ignores them) and becomes hurt when he acts offended by her perceived clingyness. Mandy later confesses to Lip that he treats her better than anyone else and deserves to go to the colleges even if it meant they would be apart; Lip is visibly moved by this. She also acted protective of Debbie Gallagher and offered to teach her self-defense 'Milkovich style' (i.e. with a half-length nightstick).