Sorry to hear your dog
is not well. Especially due to the age, you don't mention her breed, these may be signs that something isn't right. Without seeing it, the lump may be a swollen lymph gland, beginning of an infection, etc.
I suggest you take her to the Vet for an exam, blood work and a dental exam. If she has not been in fir a while, I suggest you take in a fresh stool sample, if you can get one, to be checked.