I like the idea of plowing through the brick wall. Choose your words carefully so as not to give her a lot of opportunity to go off in other directions.
"What do you mean I've never seen you as a fully functional partner? What is your definition of a fully functional partner? We've never had WHAT? I'm letting you know right now, that I don't want this and I don't want to hear about it again!"
See what I mean... keep the message simple and don't drag in the past no matter how appropriate it is. To her credit, she didn't attack your pov in her email. She allowed as how that's what you want and she respects it but you're not getting it from her. Remember, you don't have to justify your position. It needs no defending.
