Hello Abagail, I'm Dr. Deb and I'll do my best to assist you today.
I'm really sorry to hear about this problem with Kala. When a dog this size has problems with her back legs, it's obviously quite a difficult situation.
There are several possible explanations for the symptoms you describe:
1. Compression of the spinal cord by a disc or mass.
An x-ray might be suggestive but an MRI would be the better diagnostic tool for this condition.
Depending on the extent of the compression and the damage done to the nerves that go to the legs, many of these dogs can recover quite well once the appropriate drugs are initiated; these include steroids and possibly muscle relaxers and pain medication.
If this problem is suspected, the sooner she's seen, the better. The longer the spinal cord is compressed, the potential for more damage to be done.
2.Fibrocartilaginous embolic myelopathy or FCE is a condition involving necrosis (cell death) of a region of the spinal cord secondary to infarction (obstruction) of the blood supply.
The infarction is caused by fibrocartilage, which arises from part of the intervertebral disc (the shock absorbing material located between bones in the spinal column) and enters a spinal artery or vein
The cause of FCE is unknown. It is also unclear as to how the fibrocartilaginous material enters the bloodstream. Giant and large breed dogs are most commonly affected. It may also occur in smaller dogs, with an apparent predisposition in Shetland sheepdogs and miniature schnauzers. Most affected animals are 3-6 years of age and male dogs are slightly more prone to FCE than females.
Diagnosis is usually made by presenting signs, breed and physical exam although an MRI can diagnosis it as well.
The prognosis is somewhat variable...some dogs can regain reasonable function but it can take some time to do so.
3. If her signs continue to progress to involve her front legs, then there are other possible causes such as Botulism or Coonhound Paralysis or Tick Paralysis.
I won't go into these at this point since only her back legs are involved.
I would encourage you to have her seen at an ER clinic today if you can but if you can't, then you could give her aspirin. I wouldn't give her more than two of the 325 mg strength tablets twice a day (with food). I'm often hesitant to advise it's use since it could interfere with what your vet would want to prescribe but one or two doses should be fine.
I hope this helps and that you can have her seen today. Deb