I think Roy was actually being rather sadistic. It's quite clear to me that his entire intention of his apology here was to lead up to that insult, which is rather expertly delivered to hurt someone the most after they've lowered their defences and starting feeling empathy and forgiveness towards that person.

Miko, being the type of person she is, appreciates the honesty, accepts the apology and forgives Roy, and acknowledges his own recent hardship. Then, admiring even more the only person (possibly besides Durkon) in this gang of criminals who has ever shown her any kind of support or kindness, opens up with a minor flirt of her own, albiet rather stiff, formal and clumsy, but what can you expect from someone who's come from a paladin/monk monastry. (That's a double dose of Lawful Good strict formality and regulations)

And thus Roy's set the stage for what his original intention was. A quadruple combo flat-out rejection, harsh insult, declaration that he is no longer on her side and reality shock for someone with very little outside social experience. Well done Roy, I'm not even sure Belkar could pull that off.

Yes, she's a harpy. She's also a person who has been brought up and lives among like minded highly righteous and devoted people and is now escorting a group of criminals and trying to get them to also see the light and repent their actions, as she's been taught. Yes, something needed to be said, but I don't think a cruel and intentional insult was it.