So sorry to hear that tale, Graeme. Horrible in every respect and to end up with no calf and a cow for culling

If it were me, I would be doing 2 things.
Yes, personally I would not want to breed again from a cow that had had a caesarian, although some farms operate on the basis that
all calves are born this way, so I expect the vet is right and it's not an especially high risk to the cow.
But the main thing for me would be to get to the bottom of why a caesarian was needed, so as to be sure I can avoid another. Lots of possible factors : breed and breeding of cow, breed and specific bull, feeding of the heifer calf that grew into this cow and of the in-calf heifer.
As far as I know, Shetlands are not one of the breeds prone to needing caesarians. Belgian Blues certainly are, British Blues less so but still more likely than many other breeds, some Limousins now more likely to.
Ex-BH had kept suckler cows for more than 40 years, and then I added a few Jerseys to the mix. He'd stopped using and breeding Charollais bulls when he was getting too many caesarians, and switched to keeping an Angus bull and using a bit of AI : some Angus but also using the odd other breed for interest.
We bought a cow from a friend's displenishment sale. She was a very nice, very friendly Limousin (a breed we mostly avoided but we'd wanted to help set our friend up for his retirement), and we decided to use a good Limi bull on her.
First caesarian on that farm for 20 years...
Another farmer was with us when the vet pulled the strapping great calf out of her. We named him Side Door, lest we forget how he entered this world...

A few months later, said visiting farmer called wanting the details of the bull we'd used. I had made a note in our book to make sure we didn't use him again, so looked it up and passed them on. That farmer used that bull on his new herd of British Blue crosses... :/ And yes, had some caesars and some losses - but was only interested in the ones that survived and made top dollar at the mart. Not our way of farming. (Side Door did fetch more than any other calf ever sold from our farm, and the whole story left a healthy profit even after accounting for culling the cow and paying the vet bill. But it was not a story we ever wished to repeat.)