It seems this is more an issue of your confidence than anything else. A relationship should be based on equality, not you thinking you don't deserve her etc. While I'm pretty sure any guy would be feeling nervous in your situation, especially given that she's done it before, you still have to try your best not to let this mess up what you have. There comes a point in a relationship where you put your heart on the line because you trust the other person not to mess you around. It's a risk, but if you're in it for the long haul then it's necessary.
My advice would be to, as you have already done, make it clear you won't stand for any cheating, and then just tell her to have a good time and try to distract yourself for two weeks. Go out with friends, or get more hours at work, anything to keep busy! Having been in your girlfriend's position (although perhaps less of the beautiful stuff), I can tell you it is hard.. you do get offers and the club reps are always encouraging stuff like that to go on, but she CAN have a good time without cheating. And if she really loves you then that's what she'll do.