A friend got annoyed and put her angry on me. But when i get annoyed she's mad at me?

So i dont know what really is the problem. But one of my friend was in class with me and another friend. And she got annoyed at the project we were doing because she doesnt get whats going on, or something like that. And she act very cold toward me and the other friend as though we did something wrong. And well, we got annoyed at her attitude and didn't bother to ask her if she's ok and whats wrong. But the difference between me and the other friend was that the other friend would till answer her when she speaks, whereas i just act like i don't really know her, but not being rude. Well, when we were leaving me and the other friend hug her, and she just stand there like go away bi*ch and didn't hug back. That night, that other friend told me that that friend send her an apologise text . But then when i checked mine, i saw her ignoring my messages. So what is the problem here. If i ask myself, i dont think i did anything wrong. I feel like she just need to control herself. But then why is she ignoring me when she apologised to the other?