As Pat says, it's partly boredom. It sounds like she had been crated for an extended length of time in a small crate. I usually saw this previously in stressed, bored dogs that had no life outside of a small environment. It is hard to cure. Try gently touching the inside of her body where she is circling and distract her by walking. It takes a long time. This, as you said, does not occur within the three weeks at the shelter, it takes much longer to ingrain it. She also could have had head trauma, which I have also seen lead to the circling. Kudos to you for trying to help her.