A Kryptonian Power Girl having a super-powered baby might be a good idea, but I can't think who the father would be. In fact, do any of these women currently have any sort of intimate relationship with a male?
I think I've heard that once IC is over, the DCU will leap one year forward in time and pick up from there. So that would explain all kinds of out-of-the-blue changes that might otherwise require some build-up, like a pregnancy. The missing 12 months would give Kara...or any of the others...time to find a beau, get pregnant and bring the child to term, all "off-panel" as it were. So the father could be someone who's not even invented yet.
And don't forget this is DC, so there's always rape.