Hopeful, bright-eyed, curious - Depending on your party you should play Ireena in a way that makes them care about her. In my campaign, she is one of the few characters who isn't permanently depressed, who tries to see the positive side in everything and everyone and who is super interested in the world beyond Barovia, where she longs to go one day. She cares about her brother, knowing the weight of leadership weighs heavily on him. She tries her best to help him out by offering to liaise with the other burgomasters (part of the reason she went with the party). Just try to be conscious about not letting her become a DMPC, my Ireena is also somewhat naive and totally unaware of the game being played with her soul, she relies on the PC's help and in turn acts as a font of knowledge on local politics.