As I read it, your girl is not vomiting and her stool is dark possibly indicating blood from the small intestine. She is not drinking, but is willing to eat meat. Meat will cause a dark stool. She does not want to, but is able to walk, but doesn't use her hind legs correctly.
Has she urinated? If you press on her abdomen, does she splint or seem painful?
Check her gum color. It should be pink, not white, gray or deep red. Press on her gums just behind an upper canine tooth for about 5 seconds and then remove your finger. The color where your finger was should be white. It should return to pink within 2 seconds. If it is longer than 3 seconds, the capillary refill is slow indicating poor perfusion of blood. The most likely causes are dehydration and decreased blood pressure.
Assuming gum color and capillary refill are normal, she still has no vomiting or diarrhea, her Cushing's has been well controlled and she is able to move... she should be OK to wait until tomorrow to see her regular vet.
It sounds like she may be painful. This could be due to a number of causes. in the absence of vomiting, kidney infection or calculi, constipation and back pain would be the most likely causes. Determining the actual cause requires an exam and appropriate diagnostic tests.
Let me know the answers to my questions, other concerns that I may have missed and follow up questions.