Excision
(2012)

Pauline (AnnaLynne McCord) an alienated, disturbed high school student is searching for acceptance by her family. She is surrounded by a spineless father Bob (Roger Bart), a spiteful mother Phyllis (Traci Lords), and Grace (Ariel Winter), a sister she adores despite her taking more after their mother. Pauline is obsessed with being a surgeon and haunted by weird, violent, sexual dreams. As the days pass, Pauline becomes more and more delusional.

When she overhears her mother saying her sister will need to be on the transplant list for her Cystic Fibrosis, Pauline sets out to carry out an unthinkable plan. One day while her mother is away, she drugs her father unconscious. She then kidnaps her bratty next door neighbor Kimberly and also knocks out her sister Grace. Pauline shaves her head, then takes Grace and Kimberley into the garage and begins her surgery. She cuts out Kimberley's lungs and puts them into Grace. However, it is clear that her delusions have overtaken Pauline; she is not using sterile equipment, respirators, or a team to assist her in the process. Her switching lungs is a futile effort as without proper medical procedures she has just effectively killed Kimberley and her sister.

Phyllis comes home and finds Bob tied up. She eventually finds Pauline in the garage, next to the two dead girls. Pauline asks her mom to look closer and see how well she did, still not realizing what she has done. Phyllis screams and rushes her daughter, before eventually beginning to hug her, because Pauline is still her child and she realizes that her neglectful nature to Pauline's problems has in part led to what happened. Pauline begins to cry as well, apparently having a brief moment of clarity in realizing she has just killed her sister. Phyllis screams one more time and the screen goes black, leaving what happens next unknown.

Thanks Spectre!