Have Cat Questions? Ask a Cat Vet Online.
Hello. I'm sorry to hear about your cat.
At this point, it sounds like she is going to die tonight if you don't take her to be seen. The fact that she is stiff, means that she does not have much energy (ATP, glucose) left in her body. The twitching is likely from low glucose and having hypoglycemic seizures. This will eventually lead to her going into a hypoglycemic coma and dying.
Most ER vets will do a euthanasia at no charge if the patient is suffering. That may be your most humane option here.
If you want to try to get her through the night, you need to get fluids in her- water every 2 hours. You can add some sugar to the water to help with the blood glucose.
I'm sorry for this situation. Let me know if you have any other question.
I would give her 1 ounce (30 mL) every 2 hours if you can.