Power Girls has always been a problematic character for a number of reasons. A Supergirl analogue from an alternate reality called Earth 2, throughout the years DCs creators and editors have struggled to find away to visually distinguish her from the main Supergirl (it's complicated). Her designers originally decided to go for a costume that was completely different in look and feel. And when Power Girl first appeared in All Star Comics #58, her costume became iconic immediately: a white bathing suit that covered her shoulders and arms with a hole was cut in the middle, exposing her cleavage. Yes, the boob window was there from the beginning. In fact, Jimmy Palmiotti, a long time writer of Power Girl, tells the story of her creation saying:
"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 Im going to draw the tits bigger until they notice it. It took about seven or eight issues before anyone was like hey, whats with the tits? And thats where they stopped."
So yeah, the characters was literally the creation of the male gaze. As if that wasnt bad enough, in JLA: Classified #2 Power Girl says to Superman, The first time I made this costume, I wanted to have a symbol, like you. I just I couldnt think of anything. I thought eventually, Id figure it out. And close the hole. But I havent. The implications of this statement are as shocking as they are sexist: the symbol Power Girl resorts to using is a hole exposing her breast. Even she cant think of something else that defines her.