If I have people on board who have not sailed with me I sit them all down in the cockpit before leaving the dock and let them know that I am the captain and if I issue an order they must follow it without question. I let them know that the ultimate reason for this is everyone's safety.
I have been on some very contentious racing crews where the owner was not the skipper and just who was seemed to be an open question. Never a good situation and one that always will lead to heated arguments and confusion at the least.
So let them know right at the start who's is captain and boss. If you are the owner and not the captain then fine, so long as everyone aboard knows who is.
The newbie mistake you made was allowing for any question at all. Issuing direct orders is the job of the captain, however, that can and should be done in a calm, gentle and patient manner.
Your difficult helm woman should know better - do not let her back on board.