I think the switch up to 14 will be fine. If she's throwing a 12 around like it's nothing, 13 isn't going to feel much different, so I wouldn't worry about going up to 14. I'd suggest finding a different pro shop then too. And as far as balls go, gotta pay attention to her style and find a good shop that can recommend one for her, because none of us have seen her bowl. And don't go diving into the bargain bin, most of the worst decisions a bowler will ever make begin with the words, "man, look at the deal on that ball!" By the time you end up fixing the mistakes or damage, you'll spend much more than you would have just getting quality to begin with.