Yes, I am still checking. I tried to get this written before you went off line, but didn't make it. I will be away for several hours and back again after that and available to help.
Dogs love frisbee and it may well be the number one cause of cruciate injury. If the cruciate is torn, surgery is the best treatment. It is expensive and medical treatment will allow the dog to live comfortably is surgery is not feasible.
Surgical repair is followed by 8-12 weeks of restricted activity. Medical treatment requires life long attention to making sure she gets exercise, but doesn't do any jumping or fast running and turning.
It will take longer than 6 days to see significant improvement for cruciate injury. Pain control should be rapid, within a week. Gait abnormality may not improve without surgery. Limping or favoring one side is likely to remain, but should improve over several months.
Cranial nerves are those that go to the head and face.
Abnormal gait can be due to pain/arthritis or neurologic disease. Balance and movement are coordinated in the cerebellum. lesions in this part of the brain produce proprioception (positional) abnormalities, weakness, stumbling , falling, spastic movement, etc.
The walking on eggs (glass) could be due to a central (brain or spinal cord) lesion or it could be due to pain. This is what your vet meant b y f/o cruciate vs cranial nerve compression. My guess is that s/he meant to write spinal nerve compression rather than restricting it to the actual cranial nerves. Given the laxity of the stifles, pain at that level is likely.
Follow-up diagnostic testing might answer questions on the actual source..... or might not. Contrast x'rays, MRI or referral to a specialist (orthopedics, neurology) would be a good way to go if you are interested in follow up diagnostics. Using a specialist gets you the imaging studies and the specialists expertise. Your vet should know who is in your area.