Do you believe in Demons?

I always believed that there exists a heaven and a hell. Likewise that there is God and a devil. I also believe in angels but I never considered that there were demons. Or at least demons in this world. But now I do.
I have a very good friend. I have known her for over 3 years. We spend a good amount of time together when we see eachother and I have gotten to know her well.
One day as we were talking all of the sudden this very scary voice came out of her. It was garbled up and much deeper than her normal voice. It spoke a few sentences and then stopped. I did not understand what she said and it stopped as quickly as it started. At the time I thought she was playing around so I just dismissed it.
Months passed by and she was sitting on my bed and we were talking and once again that same scary deep voice came out. This time I was more observant as she spoke. This time I took it more seriously because when it stopped speaking I noticed that she was not joking. She did not make any facial expressions when it finished. It was like it never happened. It like possess her. Now I believe she has a demon inside of her! I don't know why it comes out or what it says. I did not say anything to her. I don't think she knows she has this in her. It worries me very much. Not because I'm scared. I want this thing out of her!!! I don't know what to do. I wear a cross around my neck. I have had it for years. It is precious to me. I want to give it to her as protection against this demon. I never confronted such a thing. But what I came to realize is that there are dark forces working against us. Very dark malicious forces. I, we, everyone needs to be aware. Protect yourselves. Ignorance is what they prey on. Educate yourself. Like I said I never believed in such things but unfortuately now I do.