Doppelganger (Mask of Murder, 1993)

The story follows Holly Gooding (Drew Barrymore), who moves from New York City to Los Angeles after being implicated in a murder. She is followed by what is apparently her evil twin. While in Los Angeles, she finds a room for rent by a writer and the two begin a love affair. After some strange occurrences, it becomes less and less clear whether the woman is in fact Holly or her Doppelgänger. She finds a roommate to share an apartment, and befriends him.

Patrick (the writer) soon starts to realize something is odd about Holly. As he spends more and more time with her, things heat up and he falls for her. Not knowing that she is as crazy as her brother Fred, who is in a psychiatric hospital after killing his own father. And when Patrick finds out that Holly's mother was murdered and she was the prime suspect, he starts doubting her sanity. But by that time he is too attached to her and does not want her going to jail. So when her brother Fred is attacked and she once more is a suspect he decides he is going to get to the bottom of it no matter what.