Final answer:
The main events that occurred in Stargirl chapters 16-20 can be found by referring to the book or summary.
Step-by-step explanation:
In chapters 16-20 of 'Stargirl', several significant events occur. However, without the specific details of the novel, it is difficult to provide a comprehensive list. It is recommended to refer to the book or summary to identify the main events that transpire in these chapters.