e: misread some of the thread and removed some redundant statements, but nonetheless, it's just a matter of some different dialogues depending on if she has wings/scales/a horse body/a penis, whatever. It doesn't sound like that big of an undertaking to me. You don't even have to write sex scenes for her: just say she's not interested in bone-zoning her own kid p:
If it was done, I'd wager the easiest and most likely way would be for her to have changed into a walking penis so she could feel closer to Vic now that he's been gone for so long. Would you want to talk to a giant, motherly penis? No.
Best point to take from this? If you want it, write it and pray out your butthole that someone takes it seriously or try to convince the people that aren't for it to write for you. Once you write a scene, you'll understand that it's not "just that easy" or not an undertaking. Even a simple encounter is a fuckton of work. It's literally anything but a small undertaking to churn something through to an acceptable point and then get it all up to speed. If it was easy, then TiTS would be stuffed to the brim with more content and worlds.
TLDR: Just pray that at the end of TiTS, they do some cheesy meme ending. Steele beats everything, finally thinks it's time to retire to a nice, sex-filled life... he settles down and hears his space-phone ringing. Picks up and just goes like "... Hey Mom" and then immediate fade to black. That's the best you're gonna get.