FWIW, I have only tried one 29er and one 69er in 2 sizes. This is mostly because few exist in my size. I'm not saying that plenty of other women with longer legs could find some that fit, it just is not happening for me any time soon.
I demoed an early edition GF the first year they came out. My test ride was on snow, so take it for whatever it is worth. It's handling excelled in snow because of the big wheels, but it was difficult to get the front end over a small log. At that time, the choice of tires and forks was nil, and being a tire whore, I dismissed the bike for that alone.
Then this summer I rode two Trek 69ers SS. They had a custom tuned Fox fork and a good tire choice, as compared to the early days of big wheels. The handling was very good and I thought it was a nice balance of roll over ease, acceleration and ability to handle tight corners. Unfortunately non of the sizes fit me very well. The small had great standover height but the top tube was too short and had a jacked up front end. The medium had a perfect top tube length but was way too high off the ground and did not feel as nimble. I was impressed with the overall performance, but also knew that it was nowhere near the the performance of the well fitted 26" Titus FS or Voodoo SS a already had.
It just does not work for me, but if other women have proportionally long legs to torso, I think they could easily find a good fit in the 29er world and jump on the band wagon. If her legs are shorter than 29 or 30, she may want to try a 69er. Equally so, she may just prefer to stay with a 26" wheel.