Nice that she thinks of your home as "her house". Is this relationship one sided? I understand compromise, and your situation isn't anything about that. You need to man up and grow a set of balls. I'm not saying be a complete asshole, but a bit more assertive and honest with yourself and her couldn't hurt. You are a grown man, hardly the position of a life partner to tell you what isn't allowed. I hate to say it, but admit how pathetic it sounds for a man to say, "that might open her up to the possibility of letting me wear diapers".
Be respectful, but for God's sake be yourself.