Have you tried out some Conqueror stories? There are several lists of this. Usually more than half have a queen/slave type thing going on.
Someone recommended phair, and if you look on the page there's the "Manor" series at the end with a master/slave relationship. I remember it being very interesting.
I would also recommend checking out some of the vampire/werewolf stories as a lot of those tend to include things of that nature
I'm afraid I've simply read too many things to have titles for everything, but I hope this points you in the direction of something you'll like.
You could try
Freedom's Heart although to be perfectly honest with you I don't remember if it involved BDSM at all. I just recall that one of the main characters was a slave and the other a noble.
A quick search came up with:
Fridayhaven't read myself, it had "Dominatrix" described as a lead character.
Grind this one is a series that starts off with light powerplay and progresses I believe. It's been a while.
The Interviewhaven't read myself, it had "Dominatrix" described as a lead character.
Passions Fulfilledhaven't read myself, it had "Dominatrix" described as a lead character.
Subduedhaven't read, title caught my eye and a quick skim shows a couple "experimenting."