The reason that people are supposed to comment on how unreasonable it is that wasting time on a boorish little goon who takes a perverse sort of pride in not learning a damned thing is regarded as a bad thing is that we're dealing with the same sort of wish fulfillment that had Becky apologize for being too good for her own good. We know for a fact that Lynn loved to fight with teachers and make their lives a seething Hell because she clearly seems to believe that admitting that she wasn't born knowing everything she was ever going to need to know was a humiliation from which she could never recover. To say that she needs help with something or has to spend time getting good at something is awful because bad people have dictated to her.
As for the people in the way of her need to be a defiant jerk who thinks that she's too freaking good to follow the same rules as everyone else, her chirpy Lynnsight about how much she resented people who got better grades than she did says it all:
The kids who were eager to show their report cards, always had good ones — no F, D, or C appeared on their neatly prepared sheets. I always tried to avoid these too-good-to-be-true types. Instead, I gravitated towards the mixed-bag students who had As in the stuff they liked and a "pass" in everything else!
Simply put, she not only thought of people as being extras in a movie starring her, she resented them for doing better because she'd convinced herself that they did it just to get her into trouble with her parents. The idea that her classmates didn't actually care about feeding her monstrous ego is not one that can come to a woman who thinks that people in Mexico staged a political protest for the sole purpose of ruining her vacation.