My friend says she believes in the devil........what do you think of this?

I din't know how to react. She said that their is abit of devil in everyone, but some people are able to withhold the power of the devil taking over their souls. She says she meets some people and knows by their character and things they say that they are 'devilish'. This freaked me out abit because she was so serious! I didn't know how to react..but I was definately really interested by what she had told me. She had a stage of hearing voices and smelling bad smells that she could sense but not through her nose. Abit like bipolar and schizophrenia. I really wonder why she believes in the devil! I'm not saying she can't I just want to know more!