She's usually like this. She has quite a bit more drama going on in her life than most people would suspect of a teenage girl. Ideally this looks like a mixture of her sense of humor, and something pissing her off...
That aside, I think your like one of very few people to actually care about what people say on irc chat. It's normally full of idiots, and I fail to see how one girl's opinion of you has deeply scarred you so. That, and you even RETALIATE


Both images show you getting butthurt and trying to get back at her. Wouldn't that just be stooping to her level? Could you not just X out of irc chat and be done with it?
Nonetheless, you are right in that the hostility is random and uncalled for. I might text her and see if everything's alright.