Eventually prised the microSD card from daughter and her phone this lunch time, to a resounding chorus of, there's NO WAY you can get things off a SD card once corrupted!
Progress report... I looked at various recommendations above, and for most the free version appeared to be a trial only. Recuva was free recovery. I had a bit of a false start downloading it to my Mac before realising it was Windows only (d'uh, RTFM Chris). Luckily our ancient Dell has a SD slot. I downloaded Recuva, tried it on the Wizard and it recovered (good news!) 3,367 files onto a folder on the Dell. Not so good news, only a few were fully recovered. Better news, all the ones I tried appeared to be viewable JPEGs. Not such great news, all were from 2019, in folder Album1.
I tried again with the manual version, and got another 300 or so from Album 12, still from 2019/20.
At this point I decided to open the drive in Explorer, or whatever it's called. Then I simply copied the rest of the Albums onto the Dell. All still old.
But then I noticed DCIM, had a look, and there are some 8,000 files in there, at least some from this year (some were .heic files that the Win10 box doesn't understand). Started that copying and went for a walk!
So, I reckon I'm going to be able to get most of these files back. So, what next? We don't really want them on the Dell, and daughter will want them back in Photos on her phone. She's supposed to be buying a new card just now. Can I get her to bring it here, and just copy these folders back onto the new card? She'd probably be happy just to have the DCIM files, as long as the oder Albums were around somewhere (there's an envelope in a drawer with one of her older cards in it that she's never looked at!) There seemed to be quite a file structure on this card, I was wondering if it needs to be formatted in the phone first?