The death of her mother and siblings is a negative event that influences Rachel.
The deaths of Rachel's mother and her siblings sets the entire narrative in motion. It is an event that also profoundly impacts Rachel. As a result, she is forced to live in Portland. The entire questioning of her identity on racial grounds takes place in this setting.
The absence of a mother plunges Rachel into a world of questioning the issue of race and its impact upon her. She is forced to struggle with "what is black" and "what is white" without the structure that a mother can offer. Being biracial, this challenge is magnified as she experiences reactions from both sides without the filter of a mother to assist. Rachel displays this struggle first hand in statements such as "Math can explain the reason there's one out of four chance that I'd have blue eyes. But it doesn't explain why me.” The absence of a mother enhances Rachel's struggle with the world and her place in it.
When Nella writes “How to learn all these things that might hurt them,” it is a statement about what her daughter will face. Rachel has to encounter these as a result of her mother's and siblings' deaths. This helps to make it a difficult event that casts a profound influence on Rachel.