“If you’re referring to Nightshade, he is not my Lord.”
Kaylin has a notable aversion to the use of "your" with people. I think she saw people basically enslaved when she was growing up - in brothels and other places she won't name. Barren probably treated her like property too. The only time she lets it slide without comment is her familiar and her work partner, Severn.
However, anyone who knows anything about what Nightshade's mark means knows it has something to do with ownership and would use the same phrase. In their specific circumstance though, it's more about her safety than anything. It's basically a big neon sign saying, "Touch her and die. Sincerely, Lord Nightshade".
