Best MILC for Shooting Figure Skating?

In a perfect world I'd agree but the OP's budget is incredibly tight. In the Canon world the difference in image quality between IS and non IS lenses is pretty small. The difference between f/4 and f/2.8 is a whole stop. This is the difference between shooting at 1/500s and 1/1000s or between ISO 3200 or ISO 1600. At the 1/500s to 1/1000s shutter speed range IS is going to make no difference to image quality, all it is going to do is add weight and $s, so for this purpose don't bother.

I would suggest matching it up with a used 7D body which has a halfway decent autofocus mechanism.  The whole setup should come in for less than $2000 (a little over the OP's budget but reachable) and should give her daughter a chance of getting some keepers while learning the techniques of sports photography.

Ian