Responses
I'd say that stella character's interactions at the beginning were like, she dealing with nosy strangers that (probably?) wanted to mess with her. It's just after all those events that we get to see stella open up to us as a character. wouldn't call that acting out of place really.
She's a bit of an airhead, which makes her annoying sometimes, but imo it's quite bearable.
I feel that Stella's change in chapter 80 is out of her character and does not flow of the rest of the story. . . seems out of place