@amber123 can you try soaking some of her normal pellets in hot water, then let it cool down & see if she'll eat it off of your finger or a spoon - if you have no syringes available or are not confident syringe feeding her without aspirating her?
it'll probably be messy, but she needs to keep her gut moving/digesting food.
have you tried a handful of grass/dandelions or some veg chopped up/favourite foods to tempt her to eat?
sounds like a URI if stodgy eyes /clogged nose, etc
can she breathe properly? maybe have a cloth with olbas oil on it near the hutch/cage (out of reach of your guinea) that may help clear her airways to ease breathing & make sure her bedding isn't damp or dusty.
the puffiness is often a sign of pain, if she;s fluffed up & hunched in a corner she needs Pain relief ASAP. are you vets guinea savvy as if the teeth have been trimmed & there are burrs left or not been done correctly she could have a dental issue thats been made worse by the tooth treatment.
please get a vet to check her over & prescribe any medication needed. i've had guineas in the past that have recovered fully from URI's but she will need to be seen swiftly to give her the best chance.
has she been eating properly since having her teeth done? this could be part of the problem/try strips of food & see if she mouths it or eats it.
tempt her with different hays if possible.
healing vibes being sent. for a full & speedy recovery.

xx