Rev. Mel, the first thing I want to say is this: Your mom must be a pretty amazing woman, overall. She
did make you, and I think I speak for all of us when I say we're glad of that!
In this case, though, I do think she dropped the ball. First, as Taylor pointed out, it's not a matter of "letting." Second, if your husband supports you and loves you, then he
is a "real man." A real man is strong -- and that means strong enough to value you over convention.
It sounds to me as though she's in the process of getting her head around the trans issues, and a lot of ideas and notions must be going through her head. Some of these might well slip out of the mouth. Some of these, she may keep, and others may pass. It's a process, not an on/off switch.
If we were in the same room and discussing this over a cup of tea or a glass of beer, my next question would be, "How consistent is this with her usual way of thinking?" It sounds like this comment hit you hard because a comment like that is not characteristic of your mother. If that's the case, then chances are good that she'll come around eventually. But if her worldview includes homophobia, then your being trans is likely to be much more difficult for her.