Sorry to here your little piggie is still having problems eating after her dental. This is very common, they loose confidence, there’ve tried to eat for some time and failed so they basically loose the confidence to eat and eventually just give up. Also her mouth may be sore, she may have ulcers too. In my experience I would get some metacam down her. Ask for dog metacam and talk to your vet about prescribing her a good dose around 0.3 gms twice a day. You need to step in with syringe feeding every 2-3 hours giving about 10 mg at each sitting (give her a last feed before you go to bed and then another around 6.00 am if you can) and also try offering small bits of grated veggies or tiny amounts of grass (if she doesn’t normally eat grass as part of her diet)
If you see no improvement within a 3-4 days then I would get a referral to the Cat and Rabbit Clinic in Northampton, you need to see either Simon or Kim Maddock. They are general vets and not expensive. Your vet may be on the recommended list and very piggie savy but to be honest the go to vets for dental problems in the UK is Simon Maddock or his wife Kim. There are actually very few vets that get enough experience of performing guinea pig dentals to make them proficient and get good results. Simon or Kim will diagnose what’s wrong and do any dental work consciously there and then, it’s worth every mile you need to travel.
I used to travel a round trip of 600 mile from Cornwall for regular dentals for my Ted, I never regretted it, after local vets made such a mess of his teeth. Simon got him eating hay after the first dental Ted was given, amazing results. Guinea pigs teeth are extremely difficult to get right once they’ve gone wrong and a piggie will not eat if things don’t feel right or there are still sharp spurs or uneven surfaces on their teeth. Vets can often cut their incisors very short too, this also doesn’t help your piggie to eat either
Good luck, hang in there