Is that only for girls?? It seems strange to me...There is quite a bit written on this on the forums.
The basics and what I would suggest in my experience is that unless you are over 6' tall I would stick with a 26" unless you have a fair bit of upper body strength to throw it around corners.
You're not the only one, at least two of the podium getters are up-grading there SS rides to 29ers, one already rides a geared 29erI've been 'told' that size doesn't make a huge difference on a 29er and given that I'm picking up one very, very soon, I'm hoping it's true.
I also spent the weekend at the Singlespeed Champs at Newcastle and there were a number of females riding them there. And some of those were rigid!