What is the name of that movie where a little girl befriends a mental man and her mom is an alcoholic and is killed in a car accident and then finds out her sister is her real mom?

The movie you’re describing sounds like "The Road Home" (also known as "A Road to Home"). In this film, a young girl named "Lila" befriends a mentally challenged man, and her mother struggles with Alcoholism. After her mother is tragically killed in a car accident, Lila discovers that her sister is actually her biological mother, leading to emotional revelations and family dynamics.