From what you said, your mother is not so disgusted that she'd want to disown you. It sounds like maintaining a relationship with you is important to her, and in her own mind, she thinks that she's trying to be supportive of you (though not in the way that you want). Does she realize what she'll lose if she lets this kill your relationship? It's not a rhetorical question; a lot people haven't thought about the implications when their loved ones come out to them.
My mother reacted in a similar way. I'm MTF, and she actually suggested that I should take male hormones to feel more like a man instead of female hormones to be more of a woman. But after several months and plenty more serious talks between us, she seems like she's starting to accept my transition. In the end, having a relationship with me and wanting me to be happy was more important to her than her prejudices or preconceived notions.
