well i usually don't draw people in happy situations, or any situations at all. i mean, usually i draw simple character designs so the people are just as they are, nothing to make them smile or frown, unless a certain expression is used as a form of characterization.
also i feel making their emotions either ambiguous or just mildly perceptible with a few special cases in between makes them more emotionally reflective if i feel happy or sad, the drawings will feel the same too.
if you were to remove her hat using any model editor you'll find she has a full head of hair. i think it's just the post processing effects they used in the cinematic that's playing a trick on our eyes making it look more like shaved stubble rather than hair. plus the camera was pretty far away when her hat was removed so it's not like any of us got a real good look.