this is the bike:

http://www.rei.com/product/798457

TrafficGT 3 medium with step through frame. Huge standover comfort. In the "mens" version the small is the only one available on sale and it's standover height is 28.3" which I'm guessing will be a might tight with 26"-28" pant size. The Traffic GT3 frame in aluminum looks exactly like the steel one I got my daughter in XS with it's 25" standover height. With the medium TrafficGT3 step through you'll get the same horizontal top tube length as the XS "mens" Traffic GT3.

This Marin Kentfield looks like a killer deal but even in a 15" frame the standover is 28.5" according the Marins website. That's the problem with 700c-27" wheels is that anything with usable standover height will probably be a step through frame while there might be an old XS small mtn bike frame out there with 26" wheels that isn't step through. The shortcoming with those is they usually have a too short of stem and the cost of getting a longer 1" or 1 1/8" quill stem ups the price unless you hunt around for one cheap.

http://www.rei.com/product/795499#