I'd agree with my countryman Tom that submssive is sometimes more denoting of a mindset than slave but sure most subs *do* express their attitude, their relation in actions and services more or less imposed by their relation. We're really talking semantics here to some extent - and the OP would be happy to check her pm box.
I know people who are or have been prominent on this forum who will see themselves as slaves even though it's exclusively a distance affair that is brought along by phone, internet or letters - and who are not really thinking about moving into a live-in relationship. That's totally okay by me.