My kitten has a tongue ulcer?

She eats just fine, she's playful, and she sleeps consistently. She drinks plenty of water. However, today we took her to the vet for her first exam, just to be safe, and they noticed she has a tongue ulcer. She didn't tell me any other information other than she needs to be tested for common feline illnesses, although she just got her shots yesterday, so I wasn't sure if maybe it was kind of just a way for them to get more money out of me (it was a Petsmart Banfield hospital). All of her behavior is completely normal, there is just a random ulcer on her tongue. Any ideas what it could be?