Teddy is a spinner (circles in place) when he is really excited. He will also do a slow circle to say "yes" to a question.
The first time I let Max loose in our backyard, he sprinted in large circles around me.
Maggie's habit might be a combination of 'normal' behavior and maybe because she had limited freedom of movement in the mill.
As long as her bloodwork is normal, no head pressing, your vet isn't concerned about neuro problems, and she walks in a straight line when you take her walking -- then I wouldn't worry.