I think it's a fabulous idea! I agree with ID that you should inform your partner of any outside activities beforehand. Not all submissives are "natural" submissives. What I mean is that some submissives have no problem being sexually submissive, like me, but that outside the bedroom it becomes a challenge. Seeing a mistress to experience what it's like to give up control when you'd rather not might give you some insight into the emotions your sub may be feeling. By experiencing these emotions in yourself, you may be better able to understand why your sub balks every now and then, and instead of becoming frustrated or angry, you can help her work through her feelings and develop a deeper bond.