The Great Gilly Hopkins (2016)

This is a bit painful to watch, but ends on an upbeat and largely realistic noted.  Gilly Hopkins has been abandoned by her mother at a very young age.  Her mother was very young herself at the time, living as a runaway and hooked on drugs.  So Gilly has grown up in foster care and has the usual rage that comes with being abandoned by your parents, whereby the anger is focused on those who are trying to help rather than on the parent who abandoned you.
Gilly gets a "final chance" where she is placed in a foster home with a woman with a bottomless capacity to love.  Gilly abuses her trust, and taunts her young charge at first, but comes eventually around to seeing just how good she has it.  That is when. a letter she wrote early on about false allegations of abuse comes home to roost.  Her grandmother comes to find and rescue her.  The situation is a good one for her, but the adjustment is hard, and the worst is that she comes to see her mother for what she is, a fragile, selfish person who has absolutely no feelings for the daughter she abandoned.  In the end, Gilly gets the best of both worlds, a real family and a foster family.  Well acted.