You didn't mention what her balances were on her cards. I would assume that they are low limit cards since they are rebuilders, but you never know.
It's never a good idea to max out a card, but if they aren't planning to apply for anything, then I think saving money by paying no interest for a while is the best way to go. Be sure, though, to factor in those BT fees vs. the interest charges. Again, as rebuilder cards, I'm sure her interest rates aren't ideal, but I would still try to calculate everything to make sure she was doing the best thing.
I recently made quite a few BTs to a higher limit card (didn't max it out!) and it has been a lot easier for me to manage. It's also a lot more gratifying to be making bigger payments, especially on a card with no interest.