Yes. You could. But you couldn't find main stream clinical and research experts to back that fallacy. And you could not point common and typical situations where and how that use to happen. And you could not explain that fallacy in a way that is in a line with main stream experts. Narcs do choose they acts and behaving. If they can outsource the costs of what they do, they use to act and behave in some ways. If they can't, they use to act and behave in totally different way. And you will find that in literature. And now I stop talking about the possibility of free will among narcs. They have it. It's very calculating & cunning.
The nature of NPD is that the person doesn't want to behave differently. It's like saying an addict could quit drinking anytime she wanted... she could, if she, in the moment, wanted to. But while the addict might not want to be addict, the addict very much wants to have the drink. Similarly, the person with NPD might wish he didn't have NPD, but he does want to do the behaviours associated with NPD, because... he has NPD.
Pretty much, and that's why I'm very uncomfortable with the notion than any mental condition can just be shrugged off if you have enough willpower--even if it's true once in a blue moon, it's unhelpful for the majority of people with that condition. That, and it sounds like (for some reason) AA is overly fixated on narcissm as the only possible reason someone might be a bully or mean to someone.
Some great comments here, however I had to go back to the original question. It does not have to be a "mean girl", it can be someone that hates your MC. Don't stereotype her into that "mean girl" bully.... It could be more interesting that you have two characters that do not like each other, you've listed jealousy as a reason, how about giving it more depth that under the jealousy is something else that is driving the hate. Could be a slight, a comment an action or actually someone else that is feeding the hate between the two. Just a thought.
The typical mean girl has something valuable to flaunt. Beauty, wealth, intelligence, famous parents, etc... but if the character is truly devious, then she might have been able to manufacture a desirable quality. Suddenly, the MC's legitimate success threatens to expose it. Uh-oh!
You know to build on this, possibly neither one of them are 'popular'? The mean girl could be someone on the lower rungs of the social ladder- but despite a shared plight something about the MC makes her angry and instead of befriending her she turns around and lashes out.
