I'm concerned that I may have bought my girlfriend too small of a bike. She's a smidgen over 5'7".

We were looking around for a few days as I really wanted to make sure she was sized correctly and got the proper fit. At the first LBS, we first tried a 15.5" Wahoo WSD which we were told was too small for her. The 17.5" Gary Fisher Wahoo WSD seemed a little large (she was stretched out a little too much).

At another LBS, we found a 17" 2010 Kona Lisa HT and ended up picking it up for a decent price. I love the frame and the components, but I have a feeling it might be a bit small for her now that we've taken it out for a ride. The top tube length on the 17" kona and wheelbase are identical to that of the 15.5" Gary Fisher Wahoo WSD which we were told by another bike shop that it was soo small for her.

She's just starting out and not a good judge of fit, and I'm not great at eyeballing it. I'm feeling really bad now as I wanted her to have the perfect fit and this is a big investment. Does a 17" 2010 Kona Lisa HT sound small for someone who's around 5'7"?

I'm not really sure what to do - should I see if I can return the bike and have them order a current year 17" Kona Lisa HT since the new one has a slightly longer top tube and wheelbase?

Edit: the 17" is the medium frame in 2010