Hello and Welcome to the forum
Can you travel? There is a good guinea pig vet in Derbyshire who deals with dental problems, it would be well worth the visit as she has all the tools to look inside your piggies mouth properly and find out what’s the problem and do the necessary work if needed or prescribe medication she needs to heal any infection
Recommended Guinea Pig Vet | The Guinea Pig Vet | England
In the meantime you should weigh daily at the same time and start syringe feeding. You should aim for 60 ml a day or as near to that if you can. Also keep on hand feeding plenty of small bits of veg and grass
Here is a link for our complete syringe feeding guide, she must eat or her tummy will shut down, please read through the links they will help you bridge before you can get her help
Not Eating, Weight Loss And The Importance Of Syringe Feeding Fibre