Well, you never told us what 'shy' would implicate on your char since being 'shy' can be manifested in different ways.
Does it mean that she'd rather read books/do 'me' activities? Then, she can focus on the utilitarian aspects of kidou. If she's outgoing, maybe she can go for the offensive ones. If she's the quieter, not-so-outdoorsy type, she might opt for defensive or offensive but not showy kidou.
Does it mean that she avoids people? A focus on hohou or defensive abilities/techs might be good.
Does it mean that she practices but just isn't keen on showing it? Good. That means that her stats can be basically anything. The crucial point is how she handles her growing strength.
There are many ways to handle it, really. The first thing is to recognize how her shyness is manifested. Is it avoidance of people? Is it fear of talking? Is it the lack of concern? The next would be to consider what 'utility' she's good at. Is she good at deciphering lines of code? Intricacies of reiatsu? History of the Gotei? Medicine? Stalking? Then, consider what might be considered 'functional' for that utility.
I'll give you an example:
Ansherina is a shy person. She's also a scaredy-cat, awkward and reserved. But she's perseverant in her studies and is knowledgeable about the human body. To reflect her shy personality in combat, she uses chiyudou (healing kidou) in unconventional ways. She also uses a lot of subtle kidou. She's high in kidou (I mean like, 80% of her stats) because it gives her the flexibility of being able to use it in her work and in combat. I imagined that she would be able to train on her weapon and hand-to-hand combat skills, however, she avoids combat unless extremely necessary.
Her ultimate weakness is her own illness, which prevents her from over-exerting herself in physical pursuits (most especially, battles). She knows her illness, what it does and how it triggers. But it doesn't stop her from pursuing what she's good at. In that case, while she has her own inherent faults, she compensates the lack of power by advancing her skills towards being a medic, because that's a function that she's actually good at.
All in all, the stat build and combat techs Sarah uses depends on you, however, it you really want it to go hand in hand with her personality, it will depend on how you'll use the stats, not the number per se.
