Have seen it called some, and not called more often than not.
The one time it was being called, the team who was called for it had their pitcher pile a small mountain of dirt in front of the rubber so her foot drug through the mountain of dirt to give the appearance she was dragging her foot.
The thing is this - if it is in the rules (and, we all know it is) and the better umpires call it as they get older - and we saw in the CWS that it is called a lot stricter as they get older - then shouldn't the umpires start calling it at U8, U10, U12 so these girls learn at an early age to break any bad habits they may have while they are young enough to be able to fix it?
The worst part is there are some coaches out there who have kids who throw illegal who will argue the point when called and come up with the mountain of dirt in front of the rubber instead of taking the time to explain to their player what they are doing - or how to fix it to help them in the long run.....
As far as how to keep them from going airborn when pitching - my DD's pitching coach has had some others who had small problems with that put a piece of paper, or a headband against the rubber where their front foot is and that item had to be drug through with them. If the item wasn't moving, or wasn't being drug then they were still going airborn.. Simple drill, but it seems to work.