You must be at the vet by now. I hope it something easily fixable. I hate suddenly finding something like that because then I rack my brain wondering how long it's been since I ran my hand over the place where I found a problem, wondering if I haven't been checking them well enough. But a problem tooth can be hidden for a long time, especially since cats can go on eating while in a lot of pain, and an abscess forms in hours.

How old is your lovely girl, Grace?