Yeah, the Mary Marvel stuff goes way back even before they made her all evil and black and dark and stuff in Countdown and Final Crisis. The virginity thing is the creepiest - Guy, Ambush Bug, Jimmy Olsen, Wildcat, Darkseid (seriously he offered to make her his concubine). She's 16 for goodness sake - that's still illegal in most states, does DC even know that? (and in the SuperBuddies series where Guy was making passes at her she was 14-15).
The only excuse they can make for all the sexual stuff is that as "Mary Marvel" she's supposed to be drawn older than "Mary Batson" is but in reality many superheroes(particularly the Morrison JLA since they appeared in the Shazam book and knew Mary Batson) like Superman, Batman, Kyle Rayner, Martian Manhunter, Wally West, Wonder Woman, know exactly how old she is (as evinced in Diana not wanting Billy in the JLA because he's just "a child) and none have told any of these adult creeps like Guy to lay the F**k off her! I really think there are a lot of adult male writers at DC (and it was all males who wrote Countdown) who have a problem with a character like Mary who's purity and innocence are an integral part of her character (since 1942!). Their solution: tear it down! Make her an evil greedy slut!
And like you said Stargirl is saved from this stuff mostly because Geoff Johns wouldn't let anyone try that with a character based on his dead sister (at the end of the last JSA series there was even a whole storyline about how Courtney's virginity made her special and saved her from ghosts or whatever) and no one at DC wants to mess with their Golden Boy.
Supergirl has her own title and is under the protection of the Superman editors. Wonder Girl leads the Teen Titans and is under the WW editors umbrella. There are no Shazam books being printed and DC for the last several years have been pushing Freddy/Shazam and Black Adam hard as if the Batsons didn't exist. So a bunch of middle-aged men with teen fantasies can get their rocks off abusing Mary. That's the only way I can read it since in the last 5 years or so they just have made her stupider and stupider, meaner and sluttier and let her do absolutely nothing heroic at all despite being as strong as Wonder Woman or Superman.