I still didn't quite understand who or what you're trying to describe.
Is it the retainer, addressing/talking about the princess?
Is it the princess, addressing/talking to the retainer?
Is it a complete stranger, addressing/talking about the retainer?
Is it a complete stranger, addressing/talking about the princess?
The princess, even in reference, would be spoken with the honorific -hime attached. Even by the retainer and the retainer's family; this would be a sign of respect.
The personal retainer would not have that title or similar. I'd imagine the honorific most likely be -san or -sama, depending on who was doing the addressing.