Ah... a nodeshell
I know how to fill.
I think the most difficult part of this is avoiding the human reaction of sour grapes. It hurts big-time, and so rationalization is a pretty tempting idea -- "ah, it probably wouldn't have worked anyway." There's a purely selfish variant of this one as well -- "if she can't see me as being all that and a bag of chips, then she's obviously not such a great person." Neither of these is a particularly good thing.
Best just to try to retain your respect for the person -- if the rejection is rather final-sounding, you know you have to convert your feelings for her into a platonic friendship; if it's not so devastating, just relax, be friends, and the possibility's still out there some time later. Besides, there must be something redeeming in her personality that attracted you in the first place, or you wouldn't respect her anyway.