I don't think you're supposed to be able to seduce her. Largely because in that moment you're almost blackout drunk and stumbling all over the place and that's not really gonna turn most people on. If there is a way I have yet to find it.
Momma Shork isn't really interested in sex for herself but for her children so if there are any preferences in play it would be theirs. I didn't even realize there were conditions on that option because I got it with no issues. It's definitely not racial because my vanilla human (female) Bimbochamp got it, it's definitely not genital-based because I tested it with my Catboi Champ and also got it and it's probably not Libido-based because the latter has basically none and still had the option.
Lots of the scenes in the game are like that actually. Some of the more minor ones are little snippets that are different based on your class/background. Some of the bigger ones include NPC's that can only get pregnant once per save so any special preggo scenes with those NPC's can only be used for a short time and once they're gone they can't be viewed again unless you do some save editing or start a new game.
Its why I can't stop myself from starting new saves, the completionist in me wants to see all the things.