Iin: is it normal that she said this?

Okay so me and this girl have gotten really close, and I thought we were maybe ready for a relationship. So, I asked her about us, and out of the blue she said she still is okay with going to the dance (yes, I'm in my last year of high school) but she said she doesn't want to lose me as a friend if we ever ended up breaking up or anything like that, she said that's the reason she was "holding back." her last boyfriend did the same thing, and ended up never saying another word to her (before that they were long time friends), so she said we should just be friends. Another thing, a few days after she says this though, I mentioned my ex to her in a skype call saying that she wanted to test her video settings on her new PC in a skype call after my call... so she quickly finished up a game she was playing so she could leave the call, she was really quiet after I mentioned her as well. So I asked her what was wrong and she went off on me, saying it's "annoying af" for me to talk about my ex (I only mentioned her twice). I didn't think she would think anything of it because she said she wanted to just be friends. Is what this girl did and said normal?