Girl, Interrupted

The story surrounds 18-year-old Susanna Kaysen (Winona Ryder) who has a nervous breakdown and takes an overdose of pills. While she denies she tried to kill herself, she does suffer from depression and lack of motivation. For her suicidal actions, she is checked into a psychiatric hospital and encounters a number of the patients on her journey to recovery.
Among those on the ward, she befriends Polly (Elisabeth Moss) who is a childlike schizophrenic who set herself on fire, Georgina (Clea DuVall), a pathological liar, and Daisy (Brittany Murphy), who cuts herself and has an eating disorder. But above all, Susanna is fascinated by the wardâs long-time resident, Lisa (Angelina Jolie) who is a rebellious, hateful, manipulative, but charismatic girl considered to be a sociopath. The two form a bond and Lisa encourages Susanna to stop taking her meds and resist therapy.
Susannaâs interactions with her new-found friends varies from sweet to confrontational, showing her to be quite human, but also a little lost on her journey through life at that point. She shows remarkable kindness toward those who are less certain about their future, but enjoys her rebellious streak and the camaraderie she finds with Lisa. The girlsâ actions range from pranks, indulging in fantasies, and mild manipulations to verbally violent attacks on one another. Lisa knows the operation and layout of the facility, the people, and how to manipulate them and circumstances to suit her desires. She is undaunted by the punishments she receives. At one point, after she disappears for one such punishment, she convinces Susanna to break out of the hospital, and they run to the home of the newly released Daisy, who is now living in a house provided by her adoring father.
Lisa has no patience for Daisy, as a rule, but isnât above using her, knowing the girl will have money and sheâll give it to them. But Lisaâs hatefulness surfaces in short order and she verbally attacks Daisy, exposing the fact that Daisy has had an incestuous relationship with her father for years, and leaves Daisy desperate and in tears. Susanna tries to smooth things over, but Daisy withdraws. Later, Susanna discovers Daisy has committed suicide, and is appalled at Lisaâs callous attitude when she searches for and finds whatever cash she can (including searching Daisy's body), and then leaves the house to go on the run.
Susanna has finally reached her nexus and realizes she doesnât want to become like Lisa. She phones for an ambulance and then returns to Claymore. She pursues treatment with her new-found positive outlook, stops feeling sorry for herself, works at her painting and writing, and cooperates with her therapyâpointing herself toward freedom and a promising life.
Just before her release, however, Lisa is returned to the facility. When she finds out about Susannaâs impending release Lisa strikes out at her. In an effort to secure her superior position at Claymore and spew hatred on Susanna, Lisa has stolen a diary of Susannaâs and reads it for the amusement of some of the patients so they can ridicule her together. At this, Susanna explodes, and angrily tells Lisa she is âdead already.â Lisa breaks down and she reveals that perhaps she has been living a lie, that she probably isnât a sociopath at all, but she is very troubled. The two are reconciled. Before Susanna is released the next day, she goes to see Lisa one last time and there are indications that Lisa is going to change after all for the better.
In a poignant summary done in voice over, Susanna says that despite the intense conflicts that arose at the institution, it still holds strong memories for her and she will not readily forget any of those she encountered there.

Question: How old is Susanna Kaysen?
Answer: 18 years old