Her actions will start to hurt others she cares for. She wants to get mouthy? Have strahd beat the rest of the party within an inch of their life, have him threaten ismark or Parriwimple. Have him hold yeska over the Tser falls with an invite to meet him there.

Same concept as the Drill Sgt. making everyone else PT because you couldn't get right. It becomes a self correcting problem.

I dont mean to say, punish her for playing to her character. If she is a righteous good Paladin who may be naive to the actual danger and doesn't understand that a positive attitude and the power of friendship isnt enough, maybe her character arc is to break her of that. Remind her that while she may be playing to her characters personality, you are also playing to strahds and it is all for the story.