Furminator Bald Spots

I bought a Furminator today to use on my three girls but one of them, Eddie, loved it so much that I just kept on brushing and, well, in certain lights she looks a little bald in places. Oops  !

I'll definitely be cutting down on how often I use it with them from now on (I've since read that once a week for 10~ minutes is plenty) but was wondering how long I should wait before using it on Eddie again? Is 1 week enough or should I leave her alone for a little longer before re-introducing it into her grooming routine?

It depends on how fast her fur regrows I guess.  If you use it in a week; i would go light and short with it.  The furminator works great; but it can scratch their skin too.  

Did it get to the point where it was taking off top coat as well? How many handfuls of fur came off?

We get quite a bit of our short haired cat, but it's always the same color (undercoat, not the color of her top fur). Also we only do it occasionally as she has to be quite relaxed to stick around for long enough.