I'm building up a SS for my sister for her college graduation gift in May and I'm completely clueless as to what gear length to put on her bike. She's pretty small (48cm frame), lives in a mountainous area, and doesn't cycle all that often (I'm hoping this bike will change that.). Having said that, she is fairly athletic and strong (very much a short and stout person).

The bike I'm building is an old Trek steel road frame with 700c wheels. Like I said, I'm going to make it SS as she will be using it as her around town commuter bike.

What size gearing would you girls (or guys in the know) guess is appropriate? (Like I said, I'm lost. I know waht gear inch I push, but I'm a 6' male who's been riding for a few years.) I'm thinking something like 39x17 or so. What size gearing are you SS/fixed females pushing? Thanks!