Help me get out of this?

Okay so finals are done tomorrow and my friend wants to go out to lunch with me and my other friends... problem is, we were already planning on going out without her. You see we were planning to drink that night and my friend doesn't drink and doesn't like it when we do so we don't invite her. If we go out to lunch then we will have to spend the rest of the day with her. And I have to get the alcohol and I cant just meet them there because that would be really suspicious and I would have a bottle of vodka in my bag. We were thinking about doing it friday night but I have to dance at a basketball game and it wont be over till about 9 and we wanted to go out to dinner so no one would see us drinking. It would be a lot easier on thursday for us. So if you can think of any way to get out of going to lunch with her without hurting her feeling it would be great to hear!