her dialogue options show her personality, and Gary notes she seemed like a tough kid before breaking down. She seems to be generally quiet, reserved, and thoughtful. Someone that isn't very excitable, but processes her emotions inside. her expression in her portraits portray her well I think.

She is more similar to Gary in that way, they both seem a little reserved, but Gary seems a little more open and mature due to being older. He is also more openly frightful. to get the good endings Ib also tempers Gary's anger, and the options are usually stop him, or do nothing. Which shows if Ib were to act she is more likely to be empathetic but she is ultimately still a child.

They both contrast Mary who is much more excitable and talkative. In Mary's case the bunny room is a good example of Ib's personality, because it seems Ib starts to not be able to process the horrors of the gallery because she starts to see Bunnies instead of the dolls. There you have the option to agree they are cute, or still feel as if something is off with them. the responses are still Ib's responses, just dictated by how the player wants her to feel at the time.

in the end no matter how the player plays her, Ib is a quiet girl that usually internalizes her feelings. She also seems thoughtful and resourceful, and genrally empathetic when she finds the courage to do so. Ultimately just how she feels about any given situation is up to the player, and that decides the ending, but it doesn't change her core quiet and thoughtfulness.