What important decision did Maddie make? Why did she have to think hard to do so?

After returning from Boggins Heights, Maddie became restless. She was remembering Wanda, her blue dress, and her house again and again. She could not even sleep. She was thinking herself guilty because she never opposed Peggy in teasing Wanda and was deeply distressed. At last, she came to a conclusion that she would never stand by one who does wrong and would not be a mute spectator. She made a decision of acting swiftly in such circumstances in future without caring about the aftermath of it.