I kept a Kerry Hill ewe for a further 2 years after having mastitis, this was a planned decision knowing she was such a good ewe, I wanted to breed from her further. This goes against all our policies, but I hjave not regretted it, although she went away after weaning this (last?) year at 7 crop.
Your ewe should be able to rear one lamb successfully in all likelihood, but obviously you will need to assess at birth. The ewe I kept had absolutely bags of milk on her one side, so I was able to keep both lambs on her for about 20 hours, which meant they both got colostrum and the idea of sucking a ewe. This let me wait until I had a ewe scanned for a single with bags of milk lambing, so I could twin the 'spare' on as she lambed. This was excellent, but maybe not all that usual. Your priority will be to make sure all the lambs get colostrum, sheep if possible and artificial if not, and then onto a ready supply of milk, if the ewe has enough milk for one, then that's grand, and if you can get the others onto a ewe, that will be ideal.
Probably the most sensible thing would have been to cull her last year, but you haven't so don't go beating yourself up about it, just have a plan in place, and the equipment you need in case you are unable to get them onto a ewe, either straight away or at all.