Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand that you are concerned about Spaz's overly nervous, hyperactive, with some stereotypical behavior personality, which seems to be worsening.
There are dogs that are born anxious, they just have a very high strung personality. But coupled with the fact that she is also the runt, very noticeably smaller than her parents and siblings, I would be concerned that there is a medical abnormality behind all of this.
Has your family veterinarian commented on her at all compared to your other pups? Have you ever brought up your concerns with them?
A possible cause of her symptoms and size is a portosystemic liver shunt, which is an abnormality in the blood vasculature that feeds the liver. This is usually a congenital condition, meaning that they are born with it, and symptoms may take time to develop in less severely affected dogs. So that would make sense with your pup's symptoms worsening over time. The liver is responsible for clearing toxins from the body and making proteins. If its function is abnormal then we can see abnormal bacteria proliferate in the gastrointestinal tract, leading to abnormal waste products (particularly ammonia) and that can seriously affect brain function.
If her liver appears small and her liver function is abnormal (abnormal bile acids test) then a portosystemic shunt (congenital abnormal liver vessel anatomy) would be a reasonable tentative diagnosis. Then she would need further testing to determine the type of shunt (single or multiple vessels as well the location of the shunt - inside the liver or outside). Treatment will be determined by the type of shunt. If the shunt is a single one out side of the liver and can be successfully occluded without raising blood pressure within the liver then surgery is the way to go.
If the shunt is involving multiple small vessels within the liver or if when the shunt is occluded blood pressure within the liver rises then medical/diet therapy is the way to go.
I'll give you a link which discusses the different shunts as well as surgery and medical treatment which I hope will be helpful for you:
And here's another that is a little more about medical treatment:
It sounds to me like your pup needs to see her veterinarian and have some testing done to determine the primary cause of her symptoms.
Please let me know if you have any further questions.