you referred to her as your girlfriend, so i'm assuming that you guys are dating exclusively based off of that. if that's the case, then she is absolutely shady and she has changed her story to you regardless of what actually did or did not happen. fuck that.
if this is just some chick that you occasionally talk to and you guys are NOT dating exclusively, then she can do whatever she wants, as can you. if that's the case, why are your friends getting involved and causing drama and this isn't even a conversation you should be having because she's free to do whatever.
but i'm assuming the first scenario, since you said you "got a gf in the last few days". don't EVER stay with a chick that is shady and does shit behind your back...
Stay Thirsty My Friends...
Be social! There's no such thing as a cold approach if you know everyone.