It "could" be a wart caused by a virus. It could also be a benign or malignant growth. To be on the safe side, I would have it checked out by your Vet.
Thank you we are going to take her in this week it's just weird ir grew so big in a day... some one else said it could be the canine version of herpes....gross
My personal opinion and oractice us that any suspicious growths should be checked out. Hope it is nothing