Leslie says we must fight bullies like Janice Avery because "otherwise they turn into tyrants and dictators". Jess is more inclined to avoid confrontation, but Leslie feels they must fight back because of "the principle of the thing" (Chapter 4). When Janice Avery unfairly accuses Jess of tripping her and gets him kicked off the school bus, it is Leslie who is more upset at her behavior than Jess is. Later, when Janice takes May Belle's Twinkies, Leslie is the one who, in keeping with her resolve not to allow people to take advantage of others, comes up with the plot to embarrass the perpetrator in front of her friends.
Despite her feistiness, Leslie has a warm heart. Later in the story, when she and Jess get to know Janice Avery and understand the suffering that underlies her meanness, Leslie and Jess develop a supportive friendship with the older girl.