What kind of assignment do you get to write these kind of things for your homework? There must have been a better way to address trust issues between Shino nad Nozomi than reading something like that in your student's homework.
It was really small so I'm not 100% sure, but I think she wrote it in a box that is labelled "free writing". So it's just writing whatever is in the students' mind to practice their writing skills, I suppose.
Goddamn I hope that little girl isn't feeling she's a burden to her mother because of all the bs her sister is saying to her.... Really want someone to throttle the big sis for that. :I
She was first introduced in Chapter 8 when Nozomi & Shino were at the supermarket. She asked what Shino's relations with Nozomi was, to which Nozomi answered they were sisters.
She reappears in Chapter 17, where Shino finds her loitering around outside. Shino finds out Koizumi lost her keys, and proceeds to help her look for them. It's revealed that Koizumi is a sister of (older) Koizumi, who was introduced in Chapter 12 as an underclassman of Shino and the manager of the school's volleyball team. Shino and (older) Koizumi has an argument, which leads to Shino being asked if she has any siblings. Shino says that she only has one sibling - a brother.
Which leads to this chapter, where (younger) Koizumi wrote about what had happened in Chapter 17, and her confusion of why Nozomi said they were sisters, despite Shino clearly saying she only had a brother.