Bolded for emphasis.
19:20, Obviously feels bad when he falls in the culvert.
17:20, When she makes him cry again and wipes his tears again, she has a very different blush going on, and earnestly apologizes to him again
11:52, Her gifted handkerchief is returned to her and she's genuinely surprised that he gave it back with surprise and faint disappointment
Yes, each time she recovers with a shit eating grin, but that support my earlier post in the other thread that she doesn't know how to handle her feelings and defaults to this behavior. For a first episode, there really is a lot of variety to the characterization. It doesn't reset from scene to scene either. Each builds onto the next.
My hot take thus far is that she's a hyper-exaggerated version of
Naoka from Koe no Katachi: A Silent Voice. She couldn't handle her emotions really well either, and invariably lashes out at the people she cares about, both friends and romantically. She's also portrayed somewhat realistically compared to Nagatoro, but they have similar actions.