I have a girl in a very similar position and posted a thread about it a few weeks ago. I believe it was Dunno who suggested it was just a matter of her being a slow twitch kid. My girl is also competing Xcel bronze. She has managed to learn a standing bhs, ro-bhs, and fhs and has a halfway decent vault all things considered (not a super quick runner either).
We have done a good amount of leg conditioning working on pushing all the way through the toes rather than off flat feet, box jumps, jumps on a 12" mat, repeated punches on spring board concentrating on pushing through toes, those kinds of things. We have also tried doing jumps up onto a panel mat (only tried split jumps, might try some others though). It's slow going, but she has shown some progress and is one of our more advanced Bronze kids in spite of the jumping issue. So there is hope! Maybe not for huge, beautiful straddle jumps or jump combinations, but for solid Xcel routines.
