White Oleander

A teenage girl's mother poisons her boyfriend, leading the daughter to be placed in foster care. Alone, she tries to survive by adapting through the only method she knows—putting on a mask and pretending that she is really needed by someone. Astrid picks up something from her "new" mother, desperately trying to simultaneously attract her biological mother's attention and see herself in this chaos.

If I were to make a list of films that are a must-watch during adolescence, I would probably start with this one.