Nice way to return the favor, huh? She's not being rational - you don't show symptoms instantly when you catch a virus. On the other hand, I do always tell people when there is a fever (my kids never ran fevers for teething, though.)
I would probably not do anything, but if I felt the urge to respond: "I apologize for not mentioning the fever. I didn't think anything of it because my son always has a fever when he has a tooth coming in, but I should have been more sensitive. It was not thoughtful of me and I will be more careful from now on. But - it's not possible to catch a virus in an hour. Most likely, whatever your daughter has, she brought to our house, not the other way around."