You don't even need the BGB, she does pretty similar damage all on her lonesome. The trick is waiting on the B3 until they are about to hit the floor, which causes the bounce to be higher and allowing Supergirl to chain heavy attacks like j3 into stand 3, which is normally impossible to cancel into Full Trait Zap off of MB Frost Breath. You can even do it off of regular moves of hers with the Tornado-y thingy.
The MB SRZ stuff is more of punish only scenarios, but you can probably hit confirm off a J1 pretty easily, and the damage is way higher than her standard fare. Hard to execute, for sure; even the frame kills I have there aren't an end all and it's easy to fudge the timing. Worth trying, though.