My 2-yr old beagle-springer spaniel has a peasized red bump on her lip, what could it be?

It looks like a blister or a pimple and I noticed it early last week. I noticed it again last night and it has grown in size. It is now about the size of a small pea. It is on the bottom lip/gum area and it is the only one. I am going to call the vet tomorrow, but are there any ideas of what it could be or what it came from? We live with my parents who have 2 miniature poodles (and 3 new puppies) and they eat out of glass bowls and drink out of a plastic one. They eat Iams dry food and Pedigree wet food (once in the morning).

hmmm.
doesn't sound too normal.
don't take any chances either.
get her to the vet right away.
good luck.