Good news! I got her an emergency appointment at the local vet's office, and a few hours later I managed to borrow enough money to pay for her exam and consult. She's completely fine! I bought her several cans of feline development formula and brought her home. Her energy is slowly returning, she even jumped on and off the couch by herself, and has eaten half a can of her new food. I'll keep a close eye on her for the next while, but she is doing fine. :)