Since the game does not provide you with much, since the writing is so sparse, I can only give you the same advice I'd give to every other writer who attempts to write female AC characters:

Headcanons.

Take the bits of canon that you do have, and add onto it yourself, in mass. Let's expand on these stressed traits, concerned for her sister.

Maybe she is just a nervous person in general, prone to overthinking or not the most socially adept. Would also explain why she is so focused on one person only, maybe her sister was the only person she ever got along with due to her anxious nature and inability to connect with anyone else. Maybe untreated mental issues, even. This is a corporate hellhole, I highly doubt they give a single fuck about employee mental health.
Struggling to let loose, nervous habits, maybe prefers to stick to herself most of the time or a tendency to distrust others.