If I'm supposed to be her best firend, why didn't she let me know about this?

[Rachel]

Do you guys go to the same school? If not she may not have thought that it was important to you. Maybe she thought it was a non-issue. Maybe she didn't mention it because she was afraid since you had not mentioned going to yours that she didn't want it to seem like she was rubbing your face in it. Some schools do not allow you to invite people from other schools, or your only allowed to bring one date and not another friend also. I would take a deep breath and just ask her. If your feelings are hurt, just ask her...If you guys are as good friends as you say you are you should be able to voice your opinion without it being a taboo issue.