The Babysitter (1980)

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