this size might work for her http://www.zannel.com/viewupdate.htm?id=64A7D3KDSH

only kidding.

the best thing to do is have her go with you. You don't know if its the right size until she's on it. And if she doesn't really want a bike to begin with she might want to pick out the style/color too.

That being said, if it's something she really isn't going to ride a lot, you might want to check craigslist.org or there are yahoo groups called Freecycle where you can get a cheep or free bike.

good luck