We didn't mean to scare you!

Buy her either a B17 (not the "s") if she is really on the tiny side, or a B68 (not the "s") if she is more average-wide or if she likes to sit more upright. Get it from wallbike, and you can return it no questions asked. You just can't lose with www.wallbike.com Bill is awesome, I've spoken to him several times about saddle issues, and he really stands behind the 6 month trial period.

If she doesn't like the saddle you chose, exchange it for the other one. These two -B17 and B68- are the basic ends of the spectrum, with a gajillion variations she can explore as she gets a feel for what she likes. The B17 and B68 are great places to start.

(the reason for wanting a wider saddle if you tend to sit upright is that the ischial tuberosities get wider towards the posterior of the pelvis, especially in women. There tends to be increased posterior pelvic tilt as the torso becomes more upright, so the parts of the ischia contacting the saddle can get farther apart the more upright the rider gets)