Just tell her exactly what you want (i.e. what you've posted here). The more honest and detailed you are, the better equipped she will be to provide the type scene you desire.
Believe me, I seriously doubt any good domme will have any trouble making the situation seem real. I say that for two reasons. The first is a judgment made from my experience scening with pro-dommes. Second, their whole business revolves around turning fantasies into realities.
Good luck and do shop around...every domme is different of course and you want to find someone that seems knowledgeable and also has experience and interest in performing the type scene you want.