I think that exploring new kink is essentially about two things: 1) patience, and 2) finding something in that kink that excites you.
If you're constantly evaluating how much she's trying, it creates a massive amount of pressure on a person who's already doing something that feels against her Read more… nature to do because she wants you to be happy. It's completely understandable and valid that you feel dissatisfied, but also try to remember that this is a person going outside of her comfort zone as much as she knows how to because she loves you. Be gentle, it's a difficult process.
Instead, what is really going to make a difference is finding the right mindset with her. Maybe she understands domming only as someone who cracks a whip and says mean things, but there are many ways of viewing dominance. I really liked Hermetic's point that being dominant is really about giving pleasure. Perhaps that appeals to her. It could also be that she doesn't like degrading you but enjoys being a motherly dominant. In that case, you might have to compromise temporarily, while she figures out which way works for her.
And definitely work together. No one should be alone in that journey. If you're burning yourself out on frustration and trying to help her, there are also alternatives to figuring this out or meeting your needs. Seeing a sexologist, going to a kink/swinger club for inspiration/swinging etc.
Good luck, I hope it all works out!

My partner is monogamous, although I had the benefit of knowing and expressing I was polyamorous before we were together.
I would suggest that you prepare yourself for the fact that it might take time, and I would offer that to him as well. Let him know that his initial reaction, if negative, is Read more… normal, and that you're here to figure out with him what works for you and which rules you both want for you to feel free to be yourself and him to feel safe. The most important thing is to remind him and yourself that you're on the same team, and you both want the same thing: for you to be happy; for him to be happy.
It might be a process, and that's okay. No one gets it first try, and you've had more time to grapple with this than he has. As long as he can accept that it might take time for you guys to figure out and for him to figure out his emotions, you will have the grace to at least work on it together as a team.
Essentially: Let him know he's not alone and you're there for/with him.