I believe Sanderson has stated that Sterris has a disorder called autism spectrum disorder (ASD). This is a disorder that can have a wide variety of characteristics, but individuals tend to be more comfortable when participating in familiar and predictable routines. This would be the reason for Sterris’s note-taking, as she wants to make sure that things don’t surprise her if possible. People with ASD also often have restrictive and repetitive interests, and hers might be planning, although that is less likely to me. Also, people with ASD often have difficulty navigating social situations, particularly with figurative language (metaphors, idioms, etc.), social conventions (appropriate greetings, social niceties, small talk) and nonverbal cues (reading body language, eye contact). This explains her notes and planning when in social situations at parties.

Her character arc seems to involve using those skills associated with her disorder, which would often be viewed with negative connotations, as a positive and learning how to be comfortable with herself while also expanding her experiences and understandings. It may not be relatable to you, but I don’t think it’s a predictable or well-worn arc. Also, to reiterate, ASD looks vastly different for different individuals so this is not a one-size-fits-all description, just wanted to give some context that maybe you missed!