Another reason could be related to a prophecy. If there was a prophecy in the fanfiction that Naruto would bring great destruction in the future, and Kushina, being a self - sacrificing mother, might think that killing him is the only way to prevent that destruction, even though it goes against her natural love for her son.
Perhaps she's under the influence of a powerful genjutsu. Genjutsu can distort one's perception and make them do things they wouldn't normally do. In this case, Kushina might be seeing Naruto as an enemy in the genjutsu and thus hurt him. Or it could be a test in a very extreme way. She might think that by putting Naruto through pain, she can make him stronger, although this is a very cruel way of thinking.
One possible reason could be a misunderstanding. Maybe she was misled by false information about Naruto being a threat to the village. Another reason might be that she was under some kind of mind control. In some fanfictions, dark magic or evil entities can take over a character's mind and make them act out of character.
One possible reason could be mind control. Maybe an enemy of the village found a way to manipulate Kushina's mind and make her turn against her own baby. Another reason might be a misunderstanding. For example, she could have been tricked into believing that Naruto was a threat to the village in some way.
It might be a misunderstanding. Suppose there's a false rumor or misinformation that Naruto is a threat during the test. Sakura, being over - zealous in protecting the village or the test's integrity, decides to take him out. For example, if she believes Naruto has been secretly compromised by an enemy and she has no other way to deal with it during the test situation.
One possible reason could be jealousy. Maybe Molly is jealous of Hermione's intelligence and the special bond she has with Harry and Ron. Another reason might be that she feels Hermione is a bad influence on her sons in some way. For example, she might think Hermione's Muggle - born status could bring trouble to the family in the wizarding world which is full of pure - blood supremacist ideas.
In the fanfiction, it could be that Kushina is pressured by external forces. For example, there might be a powerful group or individual who forces her to abandon Naruto for his sister. This could be part of a larger political or power - play scheme. Also, it's possible that Kushina has a moment of extreme emotional confusion. She might see something in Naruto's sister that she once desired for herself when she was younger, and in a moment of weakness, she decides to focus on the sister instead of Naruto.
One possible reason could be jealousy. Maybe she sees Harry getting too much attention or having relationships with other characters that make her feel left out and envious, which then turns into hatred and a desire to kill. Another reason might be a misunderstanding. Harry could be involved in some secret mission or activity that Ginny misinterprets as something harmful, leading her to think he's a threat.
Perhaps in the fanfiction, there is a plot twist where Sakura has been brainwashed by an antagonist. The antagonist could be using her to get to Naruto, knowing their close relationship. So, she would then be made to attack Naruto without her own will. Or, there could be a prophecy or some sort of pre - determined fate in the fanfiction's plot that causes Sakura to hurt Naruto, even if she doesn't really want to.
One possible reason could be some sort of dark influence or curse that makes her lose her maternal instincts. Maybe a powerful enemy targets her and in order to protect Naruto from further danger related to her, she feels forced to abandon him. Another reason might be that she is made to believe false information about Naruto, such as that he will bring great disaster to the village in the future.
One possible reason could be a mission. In many Naruto - related stories, missions often take characters away from their families. Naruto might have received a highly important and dangerous mission that requires him to be away from Kushina for a long time.