Ask her who she is

"Who are you? I was never told that there would be others here." I said in a matter-of-fact voice. And by the reaction on the girls face, I had said something either very wrong or very right. Her shock left her mouth hanging open for a moment before she pulled it shut and bowing deeply.

"Forgive me master, I did not know." She said as she knelt down in front of him. "Please, I am yours to command."

"Master? me?" I said in confusion. "what do you mean by that?"

"You are master of this house yes? I am here to serve you master."