Don't know if I have the right to reply to this, since I'm a Dom. Much of my relationship with my sub is being friends, lovers, confidantes; when we play, we move into our natural roles. As it happens, my sub is sub in the bedroom organized and strong willed outside of it. That makes for some adjustments from time to time.
Is she my slave??
Yes. But only because that is her chosen role. In this type of situation, it's a free choice. Could she STOP being my slave? Yes, if she chose to do that. However, our relationship would be permanently changed by that choice, since both of us are being "true to ourselves" when we are in our D/s mode. I am Dom, and I really think I was born that way. I didn't learn it, it is just "me."
Is she a slave? ONLY to me. So she's not "a slave," but "my slave." Am I a Master? Yes, but only to her. I am Dom always in the sexual sense, but only Master to one.
What I hear everyone saying is pretty much the same thing. She is willingly "enslaved" to me. And in a sense, as Master, I also am "enslaved," since I choose to do what she NEEDS--which is to receive what I wish to give without regard (sometimes/many times) for her "needs." It's pretty weird when you actually stop to consider it, since the subslave is in control of the relationship in many many ways. It's symbiotic, that's for sure.