Problem with my girlfriend...Need honest opinions! Thanks! :)?

Ok. So me and my girlfriend have been going out for nearly a year. We both live away from home and live in the same city. We don't live together as we are in different universities both we only live like 20 mins apart. We spend time together and less often we do our own things etc...However, today she told me that she was having drinks and a small party in hers on Wednesday night and she's having some college friends over. She's having this as she hasn't been drinking with her college friends within the last 10 weeks since she started second year. I said that I would come over as none of my friends are hitting the town that night and I have nobody to party with, also it would give me a chance to get to know some of her friends(I DON'T REALLY KNOW ANY OF HER FRIENDS YET SHE HAS BEEN PARTYING AND DRINKING WITH ME AND MY FRIENDS ON SEVERAL OCCASIONS). So I thought it would be nice to get to talk to them for once and have fun with my gf also. HOWEVER, she then started saying that "oh I don't want to be mean but it's a bonding session" and "I havent been out with them in a good while". BUT, she speaks to most of them during the week in college and what is the problem if I'm there??? Like, my presence is not going to get in the way of a bonding session with her college friends and I'm sure they would like to get to talk to me for the first time! I need to point out that we are not clingy and we go out without each other on other nights but I genuinely don't have anyone to drink or party with on Wednesday and she's acting kind of crazy about the idea of me coming over and saying "DO NOT COME OVER". Am I in the wrong or is she being a horrible girlfriend because that's what I think! ANY OPINIONS OR THOUGHTS ON THIS MATTER??? Especially female opinions!!! Thanks very much for your time! :)