Dom, I think you have every right to be pissed. IMHO, this would be like you sending her a text that claimed that Christianity is a choice (and factually, it, unlike homosexuality, is a choice) and thus can, and should, via support and corrective actions, be overcome.
If this were to happen to me, I'd be inclined to reply by telling her that you were hurt by this, and why.
I hope things work out for you, whatever approach you decide to take.
Vic, I hope all goes well for you Father's surgery, and I admire your self-control for deferring any arguments.
Alan, thank you for posting this. You aren't alone in dealing with that tactic. My Mother is 45 years older than me, so she plays the "age card" very well indeed. She isn't religious, but does have a fixation on having natural grandkids (and I'm an only child). I've come out to her on many occasions, and the reactions have varied. Usually, it takes about two weeks before she's back to ignoring the fact that I'm gay, and is back to trying to fix me up with women. (ARGH!).
Most of the time, though, we seem to just avoid the issue, which suits me just fine these days (I got tired of the whole "coming out" thing, after about the 20th time with her).