I don't blame Tiara for being nervous and untrusting around new people.
She know she's in an otome game, there is a heroine, her [future] husband is a MC and target, and she not supposed to be in this game. All of this, without knowing anything of the story's timeline or its events. She knows just enough to be worried but not enough to help. And I consider the game stuff to be the cherry on top.
Regardless of their reasons/goals, there were girls trying to hookup with Prince Aqua before he left, who may or may not give up now. 'The boy you like, went off to another country to study; and came back with a wife', Tiara is going to face some resentment from that. Nobles of unknown worth, trying sucking up to her. And some "young lords" wanting to one-up Aqua by stealing his girl. Being an otome game, stuffed full of unnecessary drama, there's bound to be that idiot.
All this is on top of just moving, somewhere completely new.
Nerves and distrust feel appropriate for right now (Day 3).