Depends on your girl.
My wife is 5'3" and we started her out on a CRF150F - that thing is indestructible, but also weighs as much as a full sized bike.
Next, we bought her a KX100 and that lets her rip around and it weighs about 70 lb lees than the 150, plus the suspension is 10x better than the 150.
She's ended up on a CRF250X that I have lowered and modified for her. She flat-out hauls the mail on that bike.
What ever bike you look at, try to buy at the higher end of what you think she can handle. My wife could flat-foot a TTR125 and would
be been unhappy with it in a couple of months. They aren't too powerful and are very small. Fun to goof off on, but I think she would outgrow it fast.