Why do you think Atwood chooses to reveal the rebellion of Moira through the character of Janine in Chapter 22?

Janine is a conformist. She does whatever is asked of her by whatever Gillead demands of her. Because Janine is considered "safe" by their keepers, she becomes privy to secret information like Moira's rebellion. Aunt Lydia tells Janine the whole story of Moira's escape during exercise class. It is through the very subservient eyes of Janine that we learn about the futile rebellion of Moria. It is this irony which gives Moria's rebellion and subsequent capture so much context and power.