@Redice
Didn't re-read everything, but maybe I understand what happened.
In chapter 3 Magari says that when younger she was frail and was often hospitalized. You may be right about her medication causing her insomnia, but what is that medication for? She may be better and stronger now, but she still needs medication.
Maybe that "auntie" from chapter 15 isn't really a blood related auntie.
Is very probable that her son was some kid she knew from her hospital days, maybe with the same disease. She survived, he didn't, and Magari keeps visiting her house out of consideration for their friendship.