Superman/Batman: Generations III #6, by John Byrne
I remember how back when the John Byrne forum first got an advanced look at this cover, there were a few comments along the lines of, "Eek, how old is that Green Lantern? It's kind of creepy seeing him kissing someone who's physically eleven." Byrne's response was basically, "Relax, it's just a cover. It doesn't happen in the story itself."
Okay, so Lara Wayne was hit by some strange bomb weapon when she was eleven, which kicked her Kryptonian powers into overdrive, freezing her aging. That was in an earlier issue.
That's her father and twin sister journeying to Mars, not her. I want to make that clear so you don't mistakenly assume the above page directly leads to the next.
Incidentally, she's supposedly heavily based on Buttercup of the Powerpuff Girls. Straight from The Byrne's own mouth. It's strange that he likes that show, since it has elements of superhero parody, and he's pretty adamant in his opinion that that sort of thing is "disrespectful."