Female Psyche is Confusing...Wouldnt mind a bit help please?

I met this girl a couple years ago and weve been great friends ever since (all in a small group of friends).Now I used to have a HUGE crush on her but nothing ever came of it. I always got some signs of slight signs of possible interest but never acted upon them. I still really like this girl, but have come to accept we will never be more than friends. Now, we havent really seen each other in a few months and now that im sort of seeing a girl, she asks me to hang out with her but when we do in a group, she acts very angry towards me, and gets pissed off with 99% of the things I do. Im confused as shes the one asking me to hang out, yet she acts this way (which is a complete 180 of how she used to be towards me - sweet, caring, etc.). can someone please give insight if they were in a similar situation or why the hell shes behaving like this? were both in our mid 20/s by the way. thanks!