Then why does she have a COMPLETELY different bodytype? This isn't a matter of "Supergirl just hasn't matured yet". Supergirl has a slim, cheerleader build. Powergirl is very curvy and well endowed, being built like an ideal playboy bunny. Ya can't even blame this on surgery, because it's more than just her breasts.
So this makes me wonder...is she REALLY an alternate version of Supergirl? Or just a "super girl"?