You can forget about Bomber Power plates until next year, Bomber doesn't have any three hole discs in stock; plus you are potentially introducing cant and lift into the equation.
What does she feel are the limitations of her current setup? If she can get the board on edge and boot out, then the bindings are probably fine, she may need a more carve specific board, the Burton Custom is an all mountain board with a middle of the road flex pattern. And once she gets a stiffer board, you will notice that soft boots and bindings can't drive enough power to the edges. I'm pretty sure with her current setup she could overpower the board. But is she? The next time you guys are going up to Mammoth, let me know. I'd like to soft boot it with you guys.