I was thinking Superman will protect Batman from Supergirl and Supergirl will protect Batgirl from Superman but maybe Batman can deal with Supergirl but Batgirl can protect Supergirl from Batman. Kinda rock paper scissors thing.
It's been awhile since I've been heavily into comics, but if Batgirl is more skilled than Batman and Supergirl is stronger than Superman then things have taken a politcally correct, ultra feminist stand in the DC universe that I would find hard to swallow.
Supergirl isn't stronger. In one of the recent issues superman put her down in one hit after she told him how powerful she was. Superman explained that she may have appeared that way because he keeps his powers in check all the time.