I'll follow up for Dr. Peter for you. I believe that you've determined the correct reason for Rosa's behavior. She still believes that she can rise and walk like a normal dog although 17 years of age and 6 months of disuse atrophy has set firmly in. Quality of life is as important as any factor when I consider therapy for my patients. I believe that the quality of her life is greatly diminished by the anxiety and frustration she's living with. In my opinion we're looking at very limited options. You might see how a psychotherapeutic drug affects her - an anxiolytic such as the SSRIs (fluoxetine, paroxetine, e.g.) - and, regrettably, you might consider euthanasia at this point. I don't see the value of an ultrasound unless it might offer a more definitive prognosis for her longevity.
Free now to run, jump and play
Or snooze in the shade on a sunny day
To sit for hours watching birds in the trees
Or to lie on the porch and enjoy the breeze
Free from sickness that made me weak
Restored to the dog that I was at my peak
You made the right choice for me my friend
Be at ease with yourself and let your heart mend
No more vets, shots or pill
And while you can't see me, I'm here with you still
For though you may think that we really did part
I'm there in your memories, I'm here in your heart
Please continue our conversation if you wish.