Suburbia

A hitchhiking teenage runaway, Sheila (Jennifer Clay), is picked up on Interstate 605 in the Greater Los Angeles Area by a woman with a toddler. When the car gets a flat tire, they find a telephone booth on the edge of an abandoned tract housing district. While the mother is on the phone, the toddler is attacked and killed by a stray dog.
Another teenage runaway, Evan Johnson (Bill Coyne), leaves his suburban home and alcoholic mother, ending up at a punk rock concert by D.I. Keef (Grant Miner) slips drugs into his drink, and the concert ends abruptly when a female attendee has her clothes torn off by the punks in the audience. Jack Diddley (Chris Pedersen) offers Evan a place to stay at "T.R. House", a punk house in the abandoned tract housing district off Interstate 605. Along the way they pick up Joe Schmo (Wade Walston), who also intends to move into the house. Joe changes his mind when he learns each resident must be branded with the letters T.R., for "The Rejected", but winds up coming back and accepting the brand after discovering his father is homosexual. He begins to form a romantic relationship with Sheila, who has also moved into the house.
The next morning, several men from "Citizens Against Crime", including Jim Tripplett (Lee Frederick) and Bob Skokes (Jeff Prettyman), drive through the neighborhood shooting at the packs of wild dogs that roam the area. T.R. kids Razzle (Flea) and Skinner (Timothy O'Brien) confront them, but the situation is defused by Jack's African-American stepfather, police officer Bill Rennard (Donald Allen). Jack, Evan, and Skinner steal food for the house by raiding the garages of a nearby suburban neighborhood, and make further enemies of Jim and Bob by disrupting their garage sale. When Evan sees on the news that his mother has been arrested for drunk driving, he collects his younger brother Ethan (Andrew Pece) and brings him to live at T.R. House, where Sheila gives him a mohawk. Sheila admits to Joe that she was physically and sexually abused by her father.
During a T.S.O.L. concert, the T.R. gang get into a fight defending Skinner. The men they were fighting with enter the concert and stab a security guard, framing the T.R. kids for the crime by using the knife to hang a flier with "T.R." written in blood. Jim and Bob next witness the T.R. crew vandalizing a convenience store. At a meeting of the Citizens Against Crime, they accuse Bill and the rest of the police of not doing enough to curb the teenagers' criminal behavior, declaring their willingness to take the law into their own hands. Bill goes to T.R. House and implores the teens to stay out of trouble. That night, Jim and Bob invade the house and threaten the teens, assaulting Sheila in the process. The next morning, the kids find that Sheila has killed herself by overdosing on Keef's drugs. Not knowing what to do, they bring her body back to her parents. When the T.R. kids come to the funeral, Sheila's father (J. Dinan Myrtetus) insists that they leave. Joe reveals his knowledge of Sheila's abuse, and a fight breaks out, hospitalizing Sheila's father.
At a Vandals concert that night, Bill shows up and warns the T.R. kids to clear out of T.R. house immediately, before their actions bring the Citizens Against Crime down on their heads, but they decide to stay. Learning of the violence at the funeral, Jim and Bob show up at the house and are attacked by the teens, who drive them off. They bring their car back around for another pass, accidentally running over and killing Ethan. Bill arrives, but is too late to prevent the tragedy.

Question: How did Shelia died?
Answer: She herself by overdosing on Keef's drugs