Woman Possessed By Demon via Glass or Mirror

by Demetrice
(Detroit)

I am trying to find a movie I saw when I was a little girl. It's a late 70s early 80s horror film, where a woman is possessed by a demon through mirror or glass reflection. It wants to possess her, but can only do it by using glass or mirrors as a doorway. It threatens to kill her family members if she doesn't agree.

Its evil spirit also affects the behavior of those who are weak. It possessed a man who was mute, and he almost killed a woman that was flirting with him by strangling her. I may not be explaining it right, but that's the best I can come up with of what I can remember.

Has anyone ever seen a movie like this before, do you know the name of it?