Well Mary's still a virgin even if they did slut up her appearance. They actually made a point of it when she rejected Darkseid's offer to be his concubine in Countdown (which made her later decision to accept his offer for more power at the end of Countdown - even when she got her "light powers" back from the Gods - more inexplicable). Mary's virginity was even made a butt of jokes. Justin Gray (one of the Countdown's so-called writers and now co-writing Power Girl) told Wizard Magazine that Mary was a great spellcaster because she was a virgin and the solution to stopping her would be and I quote “put Mary Marvel and Jimmy Olsen in a room with a lot of tequila and some Barry White CDs.”. So, yeah. Classy, no?
And Mary is actually younger than Courtney is here in these scans (she's Billy's LITTLE sister) so must be 16 tops now. I think the only reason Courtney is safe from being slutted up is because Geoff Johns co-owns the character based on his dead sister and he's DC Golden Boy. Even when they keep them virgins (like Mary) all other teenage females seem to be fair game for DC's frat boy writers.