In much of her history, she’s also quite young. Young enough to live in an orphanage in the golden age before getting foster/adoptive parents. Sometimes she’s an adult in the 20-24ish range. But it seems like every time the canon gets reset for her she’s canonically 16 again. And as such she’s almost always dressed pretty reasonably by Superheroine standards.

She almost always wears a skirt and briefs, of not shorts, tights, pants or full legged unitard. Don’t know that she has ever been depicted as particularly busty.

In fact, it is a running gag that her Earth 2 counterpart, Powergirl, is famously quite busty and confident his her body (boob window and all), particularly in comparison to Supergirl.

For comparison sake: Image