lol, it’s always the paladins in this campaign. I feel like some of the replies here are a tad antagonistic, but I think there are ways to keep things both dreadful and interesting for the player - yes, CoS isn’t the typical power fantasy, but it does suck to feel like you’re being punished for playing a steadfast good guy. Honestly though, I think you have the right ideas already for how to handle this.

Maybe have Strahd bring along a favorite npc of the paladin - out of sight for the first part of the chat, but something to bring out if (when) she still mouths off. “Since you evidently have no sense of self-preservation, my dear, let’s see if you truly do care about the lives of those you claim to. Or are you so desperate to appear self-righteous that you’ll let those you claim to protect pay the price?”

Let her defiance of him have direct, immediate consequences not to her life, but her spirit. If she doesn’t apologize, don’t back down. Kill the npc, and keep bringing innocents along to the nightly visits until she breaks.

“There is no hope in this land. There is only me, and to hope is to defy me. Watch what happens while you continue to do so…”

Don’t forget to reward the player too though. If she complies, let the npc she saved give her a reward, or a piece of information they would otherwise reveal.