I think Shirley would be a good unusual name. Julian Clairy has a bitch called Valerie, which is about the same thing as Shirley. The last dog we had I actually got to name (i.e., got her as a puppy) was in 1985 and we called her Vickie. She was a really sweet gentle Dalmatian girl and it suited her.
Why do we make pet names longer instead of shorter though? We often called Vickie Victoria, called our old lab, Bessie, Elizabeth. I'm already calling poor old Alfie Alfredo when I'm petting him, and Mollie is usually Molliedog.