Most likely an abscess, doesn't look to bad yet they may just give antibiotics and suggest a warm compress to see if that clears it up. If it doesn't, they will likely drain it and or do a tooth extraction if necessary.
If they prescribe antibiotics, Pick up some yogurt with live cultures ( NO ASPERTANE OR ARTIFICIAL SWEETENERS ) Give her some yogurt about 2 hours before and 2 hours after the antibiotic meds to help restore the good bacteria. Antibiotics will wipe out the good and bad bacteria the yogurt will help with that.
It's not uncommon in gliders 5 yrs n older, hope she recovers soon