Well, the ollowing advice may seem a little bit cliche, but if she says no, then the best you can do is just turn around and see if anyone else wants to go. One of the most untrue thing about going is that you have to be an item for a dance. Plus, the whole there are other fishes in the sea thing is all too true. When one girl simply says no, another is just wait ing for you to ask them. So, don't be discouraged.
And if they say yes, then it's okay to be relieved, but you don't have to bounce off the walls. Just be happy with the fact that you finally have someone to take. I think it is a bonus point and probably easier to get them to say yes, if they know you because I heard some ladies are more inclined to date you based upon not just looks but personality, as well. So, why not pal with her, get to know her, and see if it is worth it beforehand? Totally ignore that advice, if you have already.