This was a thin paperback, and I think the cover was yellow/gold with a b & w photo of two teenage girls taken in a photo booth. I read it in the late 70s/early 80s. It was about a girl whose best friend moves to NYC. After being separated for awhile she is excited to visit her friend there, but when she arrives her friend is now a stuck up “city girl.” I remember her friend mocking her for calling 6th Avenue by its other name, Avenue of the Americas, stating only tourists call it that. There is also a subplot abut the girl’s dog, a sweet old yellow lab (?) named Nora/Lorna. Near the end of the story, Nora/Lorna dies under a lilac bush and the devastated girl wraps her in a special towel that was used for the dog’s baths.