Hmm, abscesses can be very painful if that is in fact what it is. It's very difficult to tell without a physical exam in person though. Is it painful for her when you touch it?
In this case, I would suggest a trip to the vet for several reasons. One is that many times and abscess is the body's final attempt at dealing with infection. The infected area is just walled off so it doesn't spread. However, it's not really a great way of doing things. Abscesses can burst, cause pain, or the infection could spread into the jaw or affect multiple teeth. If it is an abscess, draining and treating it early will prevent bigger vet bills later on.
If it is not an abscess, a fine needle aspirate should be taken at the very least to check for abnormal growths. A quick growing lump is sometimes due to bug bites or other irritants, but if all of that is ruled out, a quick growing lump is a concern and should be dealt with early on.
So for peace of mind and early treatment, I would say a trip to the vet would be the best course here. Otherwise it could be a painful few weeks for your dog and not much that can be done at home.
