@Janice C Do you know what the opiods were? Sometimes strong painkillers can affect a pig, making them drowsy and not wanting to eat. Many vets automatically prescribe these when a pig seems to be in pain, but most of the time it's not needed.
Are you weighing her regularly? If she is losing weight then the amount you are feeding her is not enough and you need to feed her more. It will keep her alive and it will also give her the energy to start to fight back and get better.
If an anaesthetic was used during the surgery, which I would assume it was, this can also affect a pig. Sometimes they seem a bit worse for a few days afterwards as they'll be woozy still and in pain.
Have you been given Loxicom to use at home? She'll need a dose every 12 hours to help keep the pain at bay. Having her back teeth worked on will have been painful if done incorrectly, and it can also cause sores or cuts if the vet isn't experienced at it.
You need to be very aggressive with the handfeeding. Weigh her regularly and make sure she at least maintains weight. If she hasn't started to show interest or be able to eat in a few more days she needs to go back to the vet. If she's declining she needs to go back now.
It's worth noting that only minor teeth issues are fixed first time. It's common for pigs to require another dental in a few weeks, sometimes they need to go back regularly for months. Please be aware of this so you can arrange for a different vet to do the work if she is not recovering well.
