Thing is, technically he hasn't really enthralled her?; if we're going by her description her mind is still there but chained except when working together, being enthralled would mean she had her mind blown out and rewritten into whatever the emperor wanted it to be which is what makes them great spies. But he didn't and kept her around collaborating with her for over a decade. The extraordinary circumstances in the very least do make them long time collogues and friends in the technical sense or, if you like, in the worse case the emperor totally enthralled her, still yes, they are totally bffs and whatever more he likes because he rewritten her mind to be just so. At the very least not technically lying.
What you're describing is is still a horrible violation of a person's autonomy and a terrible position for a person to be in. Any "friendship" that could rise from that would be better classified as Stockholm syndrome.
