Nthing the baby food suggestion. When Prospero was sick and wouldn't eat on his own, I got meat baby food (he especially liked lamb), mixed it with some warm water, and squirted it into his mouth with a dropper. It kept him going when nothing else would.

Incidentally, Boopsie might find the soup easier to eat if you let it gel in the fridge for a little while.

Best of luck to you, Lis, and Boopsie.