1970's/80's Girl Possessed by doll

As I recall the girl's boyfriend wins the doll for her at a carnie game. The doll seems to start growing and taking on characteristics of the girl. A psychic tries to help free the girl from the doll.

I originally bought the book from one of those book fairs that they hold at elementary and junior high schools. Wasn't an overly thick book. I know I read the book in the 80's but think it might have been published in the late 70's.

I had this book, also. It would be nice to read it again.

Found it. It is The Doll by Rex Sparger.

http://www.amazon.com/Doll-Dark-Forces-3/dp/0553228242/ref=cm_lmf_tit_26