Jimmy and Amanda's PG is... their PG. She's the same character they wrote about back in their series pre-Flashpoint. For all intents and purposes for the sake of this book (and her guest spots in Harley's books), she's the Supergirl of Pre-Crisis Earth-2. Member of the JSA, has a grumpy cat, friends with Atlee and begrudgingly Harley Quinn.
Any questions regarding continuity should be filed under "don't worry about it, they don't."
For in-continuity PG stuff, we've yet to really get any answers.