hair growth patterns on dogs bum

We have an SPCA puppy who is now approximately 3 months old. She looks like she is definately half border collie, but I’m speculating as to her other half. She has spaniel type ears and longer legs than border collies but each side of her tail, her hair is growing in little circles - does this sound familiar to anybody?
I was wondering if her other half was king charles spaniel? I don’t think she will be a big dog.