I am looking for a book by Sharon Green that was written probably in the 1980's-90's. I was about a group of people that moved into and out of the past. They were dealing with underdeveloped people that practiced slavery. The heroine was captured and there was something like a harem. I can't remember much. I do remember that when I went looking for similar books, I couldn't find the right Sharon Green. Anybody ever heard of this book or maybe another in her series?

Thanks in advance.