Thank you, those who prayed and/or offered wise advice in advance of my meeting with M's mother. Our conversation was entirely amicable, though I'm more confused than ever as to where her boundaries are drawn. She is, apparently, a post-Messianic Jew ++ , but very anxious not to be put in any box whatsoever (something I can entirely sympathise with) ....and has had a very interesting journey thus far.
She was prepared to accept that the incarnation was something to celebrate, but not that it made sense to do this around 25th December...She is happy for me to talk about the cross and the empty tomb, but not to mention eggs as a symbol of new life...Oh, and she has invited me to a series of Bible studies focussing on prophecy, to which I didn't commit myself.
Anyway, it was all so much better than I'd feared, though I do feel pathetically ignorant. I guess the remedy for that is in my own hands.