Simply don't eat non vegan meals, it's not that hard. No need to explain yourself either. And I'd suggest washing your own dishes and may be cooking for yourself. Ask her to teach you to cook the vegan foods she knows.
Sorry, but I don't think you totally understand what my mother is unhappy with. She isn't happy that I am vegan while I am still growing, as she thinks it is effecting my mood and body as I am still growing. I am not trying to be rude.
I do:) All women want action, not talk. And attitude. You may be Ronnie Coleman but if you don't help in the house, there's probably something wrong with you. As a fitness professional, I know how extremely hard it is to convince people in things that they do not care about. Only results and action help! Therefore, help with the house (this means you are in perfect health), ask her to teach you how to cook something vegan (social moment that she will enjoy). Convincing someone that veganism is healthier is very hard. It means changing their life. How you wake up, what books you read ... Don't scare her, people don't want to change, especially after 25. And you are her boy, she wants to take care about you. Teaching you something like cooking would make her feel that she has done something for you and she will be proud with her boy.
Apart from this, do not let anyone, especially relatives, influence you. And in this world, you can make only yourself happy. You can help people but just to give them a lift off from time to time. Otherwise they will either feel pushed too hard or will grow dependent on you - either case is counterproductive for happiness.
You can, of course, tell her to go to hell but I don't think you want to treat her this way, therefore I'm suggesting the above