I used to have a yfz and loved it.If your going to buy it brand new get her a 450r.Just because the fact that they have reverse and it will be more comfortable for her.Thats just my opinion.If It was for you then just go with the yfz.Faster,better suspension,Looks a little nicer,And its a yamaha so you cant go wrong.Just go for the one she likes best.
Or the one you can get a better deal on.