Found: 1970s-80s YA novel about a witch moving in with a family

I remember reading a book in my teens that was published in the late 70s or in the 80s that featured a witchy young woman moving in with a family. In the book the newcomer tricks a teen girl into making a pink prom dress for her and the newcomer starts seducing the teen's dad. Anybody have any ideas as to the book I am speaking of?

Summer of Fear by Lois Duncan?

Summer of Fear was my first thought too.

Yes, that's it! Thank you so much! 😊