I have to say she's a carbon copy of dear Teddy (RIP). I scooped him up from a bunch of ferals and he was in a similar state. He wasn't feral but the ferals took pity on him and let him hang out with them.
Poor Teddy had such bad teeth you could smell him if he stood at your feet.
We never did find who he belonged to... but can't say I tried very hard as they clearly hadn't taken him to a vet for years.
Estimates of Teddy's age went up and up and up with each vet visit.
We made him comfy despite liver failure and he went to live with Caroline. It was his love of food that stopped Teddy from giving up for so long... Caroline even found him inside her fridge sitting on the shelf gumming the hell out of a cooked beef joint.
Teddy had 9 very happy final months with Caroline before he went to the bridge and we always remember him with a smile of pride that we could do that for him.
Dear Grace sounds and even looks the same as Teddy. I do hope she has at least some quality time before she passes and I know Teresa will try her best to get that to happen.