Hopefully my experience will help you find some inner self esteem. You are more of a catch than subservient man child.
So...almost the exact same thing happened to me. Years ago -before my current DH.
I was a (very happy) single parent of one preschool age DC. Some really good friends of mine, hospital doctors, set me up with a colleague - an anaesthetist. He was single, he'd not really dated anyone, was an only child. I initially liked him, tall, fit, intelligent - very interesting profession.
From the outset he said his Mum didn't approve of the fact I was a single parent. She was prejudiced against me because of it. I formed the impression she read the Daily Mail and was a bit small minded generally.
You won't believe the next bit.. I only met her once. Within seconds of meeting me she got out a camera and videoed me! Honestly! It was in the old days - so she used one of those little camcorder things. BF later said it was to show me to her cousin. We chatted politely but I was astonished she had done that. The only impression I had of her was that she wore clothes that were too matching if you know what I mean. Like dear old M&S matching trousers, top and cardi.
I thought it was immensely embarrassing and rude of her to film me.
Shortly after that on another weekend I'd booked childcare so BF and I could have a weekend day out together. He turned up and just dumped me out of the blue.It was on his mother's advice and was because... I was a single parent.
To be honest in terms of poshness, I felt that I had the edge over the mother! I would never video some-one like that. Certainly not some one I'd just met. Very rude! I'd also travelled quite a bit previously & had a city job back in those days. I can't remember what the mother had done but I'd be surprised if it was very much.
Her disapproval of unmarried mothers was just rather narrow/ small minded. If she was as posh as she thought she was she would have had a more expansive world view (and not go around videoing people).
The BF eventually found and married a child free nurse at the hospital and I then met DH.
The purpose of that story is you can do better than some adult still in their mother's pockets. She isn't as posh as you think with her small minded views. Who wants a prospective step Grandmother who is that controlling.
[Flippant suggestion- Why not really shock her. Ask her for coffee. Just find the most kinky femme fatale outfit you can. Some thigh boots, a teeny mini skirt, loads of make up etc etc ]