There are actually twenty-four chapters in the book. And in the final chapter—which I assume is the one you're referring to—the general mood is one of hope and optimism. After what seems like an eternity, Malala has finally been reunited with her parents. It's an emotional reunion, where the joy of Malala's parents is mixed with sadness at the sight of her facial injuries. Despite all the intensive surgery and physiotherapy she's received, Malala still lacks complete mobility in her face, making her unable to smile properly. But the note of optimism is never far away. The Taliban may have taken away Malala's smile, but they have not taken away her life or her soul. She's still the same person she always was, only this time stronger and more determined.
As the book ends, Malala is making great progress in her recovery and is already looking forward to the day when she can return to her native Pakistan. She gives thanks to God for all that he's given her, and for giving strength to the medical staff who worked so tirelessly to save her life and restore her back to health. Malala knows that there are many great challenges ahead, but she's more confident than ever that she can meet them. What hasn't killed her has made her stronger.