There appeared to be no issue with Luther's idea, after all, Kanda is a prince of a kingdom. Even though he may not display his free-spirited nature, he's still a pampered noble, always surrounded by a horde of guards and maids at any given time. So, having someone to attend to him is advantageous.
This Jiawen lady, who seemed naive, simple-minded and gentle, is naturally a great choice. Added to the fact that she had always lived here before, she could at least take care of Kanda's basic needs without any complications.
Further considerations, though, will have to depend on what the prince himself thinks.
However, Luther was more or less a righteous man. If Kanda indeed wanted to force this girl into something, he'd definitely not turn a blind eye, but he expected that at this point the prince wouldn't be in the mood for such things.
