Hello, Im not sure about the nervous thing, but certainly our dog Jasper who is 10 months old does this, and his little sister who my parents have also does this. I assumed it was a puppy thing and they would grow out of it. Jasper has got a lot better in the last month.
With the previous past of your little lady though, I dont know if this means the answer would be different for you, maybe the others will help a bit more