The vet did call back yesterday. It turns out there is something I can do for my cat: Force-feed her. They gave me some plastic syringes and told me to water some canned food down a bit, then force her mouth open and squirt a little at a time into her throat. She's not been enjoying it much, and with her squirming, the wet food ends up all over my hands, her face and chin and neck... But she is swallowing a large portion of it. She is still not getting enough food, but at least it's not NO food. Sonogram is Thursday, hopefully I'll find out what is up then.