Sounds like,.....
Deadly Friendhttp://imdb.com/title/tt0090917/A young genius moves to a new town and falls for the girl next door. He breaks the ice by introducing her to his robot pal BB. Later BB has a run-in with a cranky gun toting old lady, and is shot and destroyed. The girl has an abusive father who throws her down a flight of stairs. The fall kills her. The boy genius decides to sneak into the hospital and implant a chip to stimulate brain function and act like a pacemaker. The chip was from his recently destroyed robot pal BB. The brain chip would allow her body to heal, but instead she becomes a sociopathic killer with an electronic brain bent on exacting revenge on her father and a few other people that treated her/BB badly.
Deadly Friend(Trailer at VideoDetective.com)