Writing a fic, need some advice

So basically, I'm planning on writing a fic that takes place in AC3's era, sorta through the perspective of a human!Nemo, essentially. However, the dialogue in AC3 is pretty sparse when it comes to characterization for certain wingmen, and it's usually deadly serious, introspective, or cordial, with the exception of Keith whose interactions have a bit more levity to them, at least imo.

I'm having trouble writing Fiona in particular. I played her route awhile ago, but I don't remember any key aspects to her personality, other than 'concerned little sister/concerned in general'.

She's going to be more central to my narrative, so I need more than just how she acts in dire straits. I want to be able to write how she might act as an everyday person when she's not in the cockpit/discussing Cynthia.

How would you characterize or write Fiona?