German shepherd female 11 months old questions?

well i love her greatly and it doesnt matter what her mix is ( as far as i know and the vet knows ) she is a pure breed german shepherd, but at certain times when she gets excited or playful her tail goes into a perfect ( and i mean perfect ) donut shape and not leaning to either side. just sitting on top of her back .. but when she is calm or intrigued by something her tail goes like a regular german shepherd. she has all the colours, features, bone structure everything like a GSD. i was just wondering what type of dog she could possibly be mixed with . her tail is really cute when its curled it actually folds onto itself to continue the curl .