Thanks to everyone who played armchair vet with me. My dad took her to the doctor today-turns out she has terminal cancer in her abdomen, which is why she wasn't eating. There was nothing we could've done.
She's home now, and she's got three days before my parents take her back and put her to sleep. Hopefully she'll be able to swallow something tasty and lay in the sun for a while. Hopefully she'll be as happy as she can be for a few days. I'm glad I got to see her last week and say goodbye (I knew it'd probably be the last time I saw her). She lived a good 13 years, but I'll miss her like crazy.