[OC] Powergirl - My fists are up here

That's how Power Girl had always been drawn.

According to character writer Jimmy Palmiotti, "Okay. When the character was created, Wally Wood was the artist that drew Power Girl, and he was convinced that the editors were not paying attention to anything he did. So, his inker said every issue I’m going to draw the tits bigger until they notice it. It took about seven or eight issues before anyone was like hey, what’s with the tits? And that’s where they stopped. True story

From Wikipedia DC has tried to have a few times to give an in story explanation, such as she tore off her Superman 'S' because she wants to be herself and not use someone else's symbol. But Power Girl is quintessential unrealistic costume and body for female characters in comics.