Kindred (1983)

Penny is in her mid-twenties. For years she has suffered from the sexual assaults of her father, who is now beginning to take an interest in her younger sister. She tries to convince her mother and sister of her situation as an incest victim, but they just ignore her. The father tries to keep his secret by isolating Penny, but eventually she is old enough and confident enough to break free, though not without the emotional scars of years of abuse.