Just now seeing this. Hmmm.... could it be a bug sting? Do you have any bugs indoors that she might have messed with a little too closely? I would think if it were an abscess from a scratch from Pouncer that you would see a scratch or small puncture wound. How do her gums look underneath that area, it's unusual, but not unheard of for kitties this young to have an abscessed tooth!