My mother has a small knot located on her jaw line. about the size of a m&m. could this be a abscess from a tooth infection?

Lymph Node: It is more likely that this is a reactive lymph node from the infection. This should decrease in size as the infection resolves. If it does not or gets larger it should be evaluated by a physician.

It may be: an enlarged lymph node due to inflammation or possibly infection. It doesn't necessarily mean that she has a localized infection. If she has other symptoms that are suggestive of an abscess - then dental eval would be warranted.

Yes: An infected tooth is one of many reasons for what she perceives as a lump. Important for her Dentist to evaluate it ASAP.