Why would it matter if she was a boy or a girl to the groomer?
Traditionally, a boy or girl yorkie would have long hair and a top not.
Did you tell her how you wanted it cut? I took Percy and told them not to take a lot off and leave it long as I was growing it. Well, they cut his bangs shorter then Troys. I was sooo upset, I asked her why and she stated it was "easier to take care of" and "isn't it a boy?" I explained that one of the reasons I purchased a yorkie was that I loved their coats, and I wanted a long haired dog....in the end, I didn't pay for the cut.
Groomers can get pretty up close and personal while they are grooming a dog...how could she not have noticed Troy was a girl? I mean...even if she was a neutered male...they do leave a little something there.