The Babysitter (1980)

"She drove the mother mad. She seduced the father. Now, what's going to happen to little Tara?"

Overprotective mother Liz Benedict meets 18-year-old orphan Joanna Redwine and hires her as house help and live-in companion to rambunctious daughter Tara. Liz's husband Jeff isn't too thrilled with the arrangement, and his fears soon prove justified when Joanna begins to manipulate everyone and to slowly destroy the family. Meanwhile, next-door neighbor Dr. Linquist investigates and discovers Joanna has a disturbing past.