Can I snap at my girlfriends friend because she thinks that she's so educated?
Why would that make you want to snap at her?
I always felt that she doesn't respect me because I haven't got a high school degree
Going at her in a rude way will not help the situation out. If you have concerns, you should talk to her peacefully.
I can't, I'm really mad at her and I'm more mad that I feel bad for being mad at her.
That bad that you feel is knowing how wrong it is to hate someone just because they're a little bit annoying. You need to forgive her for her rudeness and not lower yourself to her level, because being aggressive is bad for conversation.