I was thinking vanilla? Get a really small container to try first (unless you are an ice cream nut! ).

I know adult cats aren't supposed to have milk or milk products in case of lactose intolerance - but heck, if she'll lap it up, go for it! Maybe several teaspoons a day? That'll at least add some calories and fat and some calcium.

You could ask your vet about Hill's A/D - it's used for surgical recovery and all, comes as a wet food, and is PACKED with nutrients. Too rich for normal healthy cats. If your vet approves, maybe she will give you a free can to try.