An actual demonstration of this line of reasoning could prove more effective than simply telling it to her. :)

Perhaps call her attention to some skills she hasn't mastered yet, multiplication for example. No matter how much she stares at the problem she won't be able to solve it until someone teaches her how and she has a lot of time to practice. And even if she could learn just one problem that doesn't mean she could solve any multiplication problem set before her.

Her brother has some skills that he is still learning and practicing, and others that he simply hasn't learned yet. While it's ok for her to feel frustrated, angry or hurt by his actions or choices, it is no more in his skill set to accomplish these things accoding to her desire than it is in hers to preform those problems simply because someine is telling her repeatedly to do it. And just as it would be wrong of someone to act on that anger towards her or punish her for not being able to solve them, so too, she would be unjust in acting on her anger toward him.

my Daughter is 2 years younger than her Autistic brother. It is a show and tell. It takes time but if you point out the the differences it could help. My daughter eventually started to understand.