Who has the right to be mad here?

My friend and I were having a discussion yesterday about a program at a college where you go and stay for 6 weeks for free. I was asked her how it worked and things like that. I told her it doesn't make any sense for colleges to give free classes out. She got really mad and started yelling at me about how annoying and stupid I was being. I calmed her down and dropped the subject. I had one more question a little later. It was a basic yes or no answer. She wouldn't answer it bc she said I'd get annoying if she answered it so she didnt. At that point I was pissed off so I told her she was pissing me off and she started telling me I was stupid and annoying. Today she brought it up again, once again I got pissed, and told her again how annoying and irrationial she was being herself. She stormed off; she's never done these things and I don't understand why she's doing it now. Who has the right to be annoyed here and why would she be acting like this?