I'm 5'4" and ride Small/16" - 17" frames usually. It sounds big but, if I go any smaller, my weight ends up being too far forward to feel balanced. So it's not unheard of that you might need that size....arm, torso, and leg lengths will all play into it, as well as overall flexibility. I would try riding a smaller bike, just for giggles, and see how it feels.

I like my 29er rigid, and I like my 26 full suspension...horses for courses If the 29ers fit well and feel good, then why not?