Choosing the 5 most important plot points for the entire novel is going to differ from reader to reader. There might be some overlap, but it is likely never going to be 100% identical for every reader. My recommendation is to pick the parts that coincide with a standard plot analysis. Those would be the exposition (introduction), rising action(s), climax, falling action, and resolution.
Exposition: We meet Esperanza and her family and learn that they just moved into the family's first ever house. Esperanza is disappointed by the entire thing.
Conflict/rising action(s): In one word, "puberty." That's really short changing the story, though. Sure Esperanza is growing up and learning what it means to change from a girl to a woman. She's curious about sex and men. But Esperanza is also learning about gender roles and gender inequality. She's learning about the hardships of poverty and at times abuse.
Climax: Esperanza is raped.
Falling action: Esperanza looks for a way to leave Mango Street once and for all.
Resolution: Esperanza realizes that escaping Mango Street is not the answer. Her writing is her tool to help her cope.
I hope it helps!