Yes,
@SallyintNorth I suppose you are right that I have some experience of looking after elderly sheep. What a rep to have

We have looked after several ewes in their late teens up to 20yo. And again, yes, most vets have little experience of tending to older sheep and their idea of when a sheep is 'old' tends to be very different to mine

. Soays are not quite the same as Hebrideans, which are the longest living sheep we have had, and we have successfuly bred Hebs up to 16yrs, whereas our Soay have not lasted quite so long.
Once a ewe stops breeding and no longer has that call on her reserves she can often feed herself with no front teeth at all, as your ewe appears to be doing In the Hills. Once her molars start to go though that really spells the end. There are nursing care things you can do to support a sheep in that state but really once she starts to lose weight she has started on a downwards spiral and it's best to euthenase her before she becomes miserable. Mr F shot our last ancient ewe while she was in the middle of munching digestive biscuits, which seems a happy way to go
With your ewe In the Hills, as the vet is happy to try her with AntiBs and metacam then give her a go, but if she doesn't respond then to my mind while she is still relatively happy and well is the best time to make the decision, sooner rather than later and before she has to face the winter. If she rallies, then give her a little extra feed to make up for the fact that she can't graze at the same rate as younger sheep - we use Carr's Champion tup coarse mix which is OK on the teeth (if they have any) and is nicely varied. We also give preferential grazing rights to old ewes - they get to eat in the orchard as they are not going to damage the trees being toothless, and the grass in our orchard is also varied and tasty and a bit longer than the pastures. If all your ewes are toothless then just up their feed a little. Have you tried Digestive biscuits? It can take a while for sheep to get a taste for them, but toothless sheep enjoy the gummy crunch of biscuits and benefit from the extra energy in a half digestive.
Remember, you know your animals better than your vet, or anyone on here, so use your best judgement to do what's best for her, in your situation. You'll know when the time comes.
Cross posted with In the Hills