I think her face blends into the background, and your eyes are instantly attracted to her legs. Which I don't think you want unless it's a pinup photo with slightly less clothes on. If you cropped it so that the wall was straight, I think that'd make it better too. Otherwise, nice shot.
There are some nice suggestions for improvements, hudsonp, but maybe the best thing to do is to just leave this one alone for now(?). Like you said, your model and her parents loving it is the most important thing, so just keep these thing in mind to apply next time.
Remember though, in selective color shots, the element of the photo in color is meant to draw the most attention. So here, the focus is her legs, while you generally want it to be on her face (especially for a senior portrait). On one hand, there's really no big need to change something that your clients already like so much. On the other, you could keep a copy of this version, make another one that is colored differently, and give them a choice. That's probably the best route, and I hope you kept a copy of the original!
Maybe just a few other minor adjustments are in order? A bit of sharpening would help, and perhaps a little dodging/burning (or a light vignette) would help separate your model from the background better.
i dont liek it. is over exposed, and not enough contrast between the subject and the background. looks liek somethign a teenager wuld take for myspace.