Having access to a good vet with the knowledge and experience to treat rats or at least a good vet who likes rats and is willing to learn is absolutely essential to having pet rats.
Facial swelling can be dangerous and she needs to see a good vet asap.
Since she is young it is likely a facial abscesses. Facial abscesses are very dangerous and often kill, so she needs to see a vet, needs appropriate antibiotics, and may need surgery
Check her teeth to make sure they are not too long, and have not pierced the inside of her mouth
(
http://ratguide.com/health/digestive/malocclusion.php)
Warm (not hot) compresses can help to bring an abscess to a head, but personally I would not fool around with a facial abscess. See
http://ratguide.com/health/integumentary_skin/abscess.php
You can try feeding her soft foods so that she gets nutrition and to help her to stay hydrated
Grind up some of her blocks and soak them in cool water to make mush, feed organic soy infant formula thickened with baby cereal.. Both of these will give her needed nutrition and help to keep her hydrated
Other things include: cooked real whole grain oatmeal, cooked quinoa, cooked sweet potato, cooked squash, and baby food
I hope she is soon seen by a good vet, gets the care she needs, and is soon feeling much better
