Bubba, wouldn't it be best if she changed bits for jumping , though? I have never seen anyone do jumping in a TT.
I think you need to think about what exactly is different about the TT and the snaffles to find out why the horse seems to work better under one and not the other. The tT is a broken bit, so it might also have some nutcracker affect. what is really different about those two bits? Are you changing more variables, such as mouthpiece materieal and thickness, too?
Is your horse responsive to the TT action early on, or does she require you to engage it so far that the curb chain comes into play? Meaning, is your horse running through light bit action and only responsive to the pinch of the curb chain?
I don't care for the TT bit, but if it works, there is no reason to not use it. The horse is not suffereing. ONly for jumping can I see you needing to reconsider a bit change.