At her size (close to mine) the weight of the four stroke isn't as much of a deterrent as the power of a 2 stroke would be for a beginner.
I'm 5'10" and a little lighter than her and I started out on a KLX300 and rode it for 2 seasons.
It was a great bike to start on and it helped me learn HOW to ride but, once I tried out a CR, I wanted one. Don't know why but I love the power and it certainly gets over the obstacles we encounter much easier than my KLX. It's fun to shock the people I meet too! ;)
After riding the KLX for a season & a half, I decided I wanted something a bit more challenging. I tried out a couple XR250's, XR400, KX250, CR250, YZ426F and the CR500 was my choice.
I still like the KLX but, it seems tooooo easy to ride. The XR250 seemed very similar but not as good for the steeper hills (for me).
The electric start to me is a waste of weight but then I haven't had to kick and kick and kick and kick on the KLX after it was loaded up or tipped over for quite awhile. (Secret is to full throttle the beast when it's in that situation THEN kick it HARD till it starts!) The CR is pretty much a one kick machine once it's first started.
The 4 strokes are much more forgiving in the trails. Any of them around the 250 - 300 cc newer (95 on up) would be pretty comparable from what I have seen. Anything less than a 250 will probably be pretty cramped for her.
What part of Canada are you in?