I am sorry to hear about all of Kisses' problems.
My name is Rebecca. I am a veterinarian, and will do my best to help.
I would not be ready to put her to sleep yet, if she were my own dog.
She sounds painful, and it sounds like her pain is not under control yet. The effects of the diazepam ( for muscle relaxation) and tramadol for pain should have been working in 24 hours. If this started last weekend and she is not any better, I would try different medication, or do more testing, such as an Xray of the area in her spine that hurts.
I would consider giving her some kind of medication for inflammation, like meloxicam or carprofen, in addition to the tramadol. If the tramadol is not helping with pain, I would try gabapentin next.
I like methocarbamol as a muscle relaxant more than diazepam.
Acupuncture can be helpful for back pain.
If she were mine, and was not getting better, I would consider taking her for a second opinion with a neurologist, and/or pain specialist.
You are a dedicated and committed pet caregiver, dealing with her heart disease
and Cushing's disease. I know she gives back 1000% for everything you do; dogs are just so amazing.
Please let me know what else I can answer or help with.