The lump might be benign or not……either way and especially due to the location it will probably have to be removed.
Another option, if it’s bothering her and it sounds like it is from what you describe, is to go to the walk in emergency vet, it may cost a few bucks but they will examine, diagnosis and refer you to a specialist if they can’t treat it there.
I wouldn’t wait too long or ignore it. Maybe the vet can fit you in sooner? Most vets leave time slots open once or twice a day for emergencies. Otherwise, maybe he could refer you directly to a specialist. You have 2 issues here, an abnormal growth and allergies.
