I would also say it is a hernia. Depending if its still open or not will determin if your pup needs surgery. If the bump is hard and the vet cannot push it back, then chances are they will leave it because the hernia is probably very tiny and fat has probably plugged up the hole. If they can push it back then chances are they will have to operate.
How old is she? A lot of times they fix hernia's when the pup is getting spayed or neutered.
I agree though you should have a vet look at it, they are the only ones who will know for sure what to do.
Good luck and let us know!