Hmm. It is difficult to tell what's going on. It seems unlikely that it would be an ulceration at this point, right? How long did it take to get to this point like from when you first started to notice a problem? It does look really sore and look how she is still smiling.
Maybe it's a coincidence or maybe if she got a little cut there it was more susceptible to getting carried away/infected? Sorry I don't have many answers. I'm probably asking the same question you have already been asking. I think it's a good idea to talk to the doctor who treated her, but if you are having trouble getting a response you can email one of the experts here on this site and they may be able to give you their opinion on it. Is she on an antibiotic for it anyway? Maybe if it clears up easily with that, you may have your answer. Hopefully it will get better really soon so you can put your worries to rest! Let us know what you find out! Good luck!
I love the pink mask by the way! I have 4 daughters and that mask would be a hit at my house for sure!