I am sorry to hear that your girl Kiyai is now unable to use her rear legs properly, is refusing to eat and isn't eliminating normally.
Has she ever had radiographs of her spine or hips?
If you pinch her toes on her rear feet does she feel it?
If you support her standing and flip her rear feet so the topside is down does she immediately right them?
It is important to find out whether she is too weak and painful to get up or whether she has lost the ability to do so.
It is possible that she is holding her eliminations because she cannot get into proper position to eliminate or she has loss of control due to loss of neurologic function. These dogs either cannot feel that they need to eliminate or have lost the ability to relax and eliminate.
It is possible that she is dysplastic, but I would expect her to at least have some function. Sometimes it is simply too painful to get up and eliminate. Symptoms can happen suddenly if a piece of the arthritic changes in her hip breaks off and is free in the joint, but I would not expect her to drag herself, just be reluctant to rise.
But since she is dragging herself that can signify neurologic problems, such as an intervertebral disc(s) (cushions between the bony vertebrae) that are out of place or spinal arthritis putting pressure on the spinal cord or even a mass in or around the spinal cord.
Another possibility is a condition called FCE, fibrocatilagenous emboli, where a chunk of cartilage breaks off and lodges in the blood vessels that supply the spinal nerve roots. It is very painful initially as blood supply to tissue is blocked off. The pain only lasts a short time, less than a few hours to a day, but the weakness from the nerve damage it causes it can last for weeks or in rare cases is permanent.
Rotties, Huskies, German Shepherds and other large breed dogs are prone to a disease process that affects the rear legs called lumbosacral stenosis (LSS).
It can have many of the same symptoms as a FCE as it causes neurologic symptoms too. It is caused by weak spinal ligaments that allow the bones in the spinal column to move and place pressure on the spinal cord or it can be due to inflammation of the ligaments inside the spinal cord canal causing pressure on the spinal cord leading to loss of function, just like a FCE.
FCE are initially painful but after that it's just a matter of regaining function.
LSS can be painful on and off until the spinal column is stabilized and the pressure is taken off the spinal cord permanently.
Another possibility if she seems not painful is a condition called ascending myelopathy. This is a progressive degeneration of the spinal nerves that begins with incoordination of the rear legs then progresses to loss of urine and stool control (continence). This seems very unlikely with her as her symptoms came on very suddenly according to your history.
She really needs a veterinary examination as soon as possible. Radiographs to look for a collapsed disc space, a mass, or arthritis of the spine and hip dysplasia would be helpful. We need to know what the problem is to treat it successfully.
If those look fine then an MRI of her spinal cord in the back of the body will be helpful.
Pain and inflammation in these conditions is controlled with nonsteroidal anti-inflammatories like Deramaxx or Rimadyl as well as Tramadol and/or Gabapentin.
Long term you can use the prescription drugs I listed with the omega 3's and glucosamines if arthritis or hip dysplasia is diagnosed. These nutraceuticals help improve cartilage and joint fluid health as well as reduce inflammation.
I recommend using a combination of a glucosamine/chondroitin product (examples are Dasuquin or Cosequin) and an omega 3 fatty acid (like 3V Caps or Derm Caps). I recommend an omega 3 fatty acid dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give her 20mg of EPA per pound of body weight per day. For example an 80 pound dog could take 1600mg of EPA per day. Omega 3's and glucosamine/chondroitins work synergistically and improve cartilage health and joint fluid quality and quantity as well as reducing inflammation. They can take several weeks to see full improvement but some dogs do very well with them. They are available over the counter.
Another option for long term supplementation is a product called Duralactin. This is an anti-inflammatory product derived from milk proteins and it also has omega 3 fatty acids incorporated into it which can be very helpful. See this link for further information: http://www.duralactin.com/products_canine.html
There is no treatment for myelopathy, unfortunately. We can only truly diagnose that condition after death because it requires a biopsy of spinal cord tissue. We usually rule out everything else and with a history of little to no pain and a gradual onset then we assume it is myelopathy. There is a blood test that looks for genetic markers for the disease which is pretty accurate if she has the form with those particular genes involved. If you want to test her for the disease here is a link to a website which will give you information about how to get her tested: http://www.offa.org/dnatesting/dm.html
If she starts medical therapy and is not responding to cortisone or nonsteroidals then I think that more diagnostic testing should be done. An MRI of her spinal cord will help diagnose intervertebral disc disease or lumbosacral stenosis. Those conditions can be treated surgically.
In the meantime try and keep your pup quiet. With spinal instability the more they do, especially jarring activities like trying to pull herself around and stairs, the faster the condition can progress.
In case she has an accident putting her on padded, absorptive bedding is best.
Please let me know if you have any further questions.