It almost looks wart-like... how old is she? Canine Papiloma Virus (CPV) aka "Puppy warts" comes to mind.
Is that the only bump? CPV tends to travel in groups. Denna had it as a puppy - when she was 6-7 months old - and had maybe 6-12 warts, total. We used Thuja and Lysine along with her good diet and lots of rest... no visiting with other dogs (CPV is highly contagious among puppies). Hers cleared up in about 5 or 6 weeks, as expected, no vet intervention required. But... make sure that's what it is first... that one bump could be something else, too.
Here's one site that discusses CPV:
http://tails-a-waggingdogblog.blogspot.com/2010/02/canine-papilloma-virus.html