Since femdom is quite a big of an umbrella term which hides various kinks underneath I guess you could receive a lot of various ideas. Looking at your game I don't see it as a particularly femdommy game so personally I think one option to go is with the footdom. It is one of the most popular and most often used kinks (and foot fetish is fairly widespread too) and I believe it could be suitable as I don't think you want to go for something strong. Some kind of (sensual) foot worship scene with sniffing (maybe shoe/sock worship sniffing) with framing the domme from the lower angles, with MC/sub maybe laying on the floor (she can place her leg on him at some point as a visual cue to their D/s relation in the scene) or kneeling. Mixing that with some verbal humiliation should work as a basic femdom scene imo.
If you want more there's a ton of stuff you can try: beating, trampling, face slapping, whipping, ballbusting, cock torture, electro shocks, spit and/or snot feeding, pegging, pee drinking or simply peeing on a sub, petplay, ass worship, sub as furniture, various levels of verbal humiliation, armpit licking etc., to more hardcore stuff like scat or mutilations or forced bestiality, all three of which I'm not a fan of btw. I guess you can see if there's anything that you find even remotely interesting/arousing (to make working on a scene smoother plus usually the scenes came out hotter if they're based on the dev's own kinks imo) as I guess you're not into femdom yourself and you can also check if any of these suits the characters and your novel (and your supporters). Also - I don't know - but if one of the reasons to add such a scene is to bring the femdom lovers to your project I don't think many of us will come and read/watch your novel; and by no means I'm saying this to be rude.
