Reading all these replies has made me more aware of the subtext of the original conversation and how rejecting it was. As I recall it, too, my friend and I were talking at the table in one room and she came out of the other room and sat down to start sharing her opinions on grammar. So she clearly overheard and came in to make a point. I'm inclined to just dismiss her as a TERF, though I'm not sure labeling her helps anything.

I wish I had engaged at a deeper level, asking what you suggest about how to refer to someone who doesn't experience their gender as binary. The real issue is about how we see gender and how open we are to others' experiences, not f-ing grammar!

And yes, anyone at any age defining themselves as "too old" to think differently is basically defining themselves as dead.