A slave is one that has gathered into a contract with a master whether it be written or verbal. She is therefore the ownership of the master and has no rights. She might build up to rights but that is between the contract and the master.
A submissive is truely the one in charge when in a bdsm relationship with a dom. He might be dominating but she gives the clues whether it be too hard or needs to stop or slow down by words and notions. A submissive woman is never owned and has her own mind to think and plan.
That is why I am a submissive woman and not a slave.