My friend told me she's been thinking about how she's better than everyone else and that she could possibly be God. I thought this wasn't a huge deal and tried to keep her in check by teasing her a little bit. (I realize now that I shouldn't have done that, that was really shitty of me.) She'd say things like "You're just jealous" or "You're inferior to me" and I'd respond with "Yeah ok" or "Keep telling yourself that." I said "I could knock you over like a bowling pin" and she said "I could kill you." Thinking she didn't mean it, I said "Go ahead, you know where my house is." 

The reason why I treated this the way I did was because it was so out of character for her. She's usually pretty nice and chill. I figured she was just riding a wave of superiority or simply just joking. Still, I shouldn't have egged her on like I did. 

She then continued to talk about how she could kill her family because they were beneath her and then I guess she kinda snapped out of it? She said she didn't want to kill anyone, and she said "Make it stop."
I then realized how serious this was and didn't know what to do. She apologized for what she did and said she was having a sort of episode. She referred to this sudden wave of superiority as a god complex. I tried looking up stuff on google to see if there was anything I could do in case she starts acting like that again, but I couldn't find anything all that useful. 

I guess what I'm asking is what should I do if my friend starts acting like this again without making things worse?