So she wants to go to a different high school...she doesn't even know Tomo is the motive so I don't see what crime she's committed. Your kid is working hard, trying to improve their grades so they can go to the school they want, isn't that something you'd normally encourage? From what I remember it seemed like Mirei did have some issues in the past with people approaching her and such but I feel like her mom has some deep seeded fear or control issues.
Edit: came back from next chapter, ok I understand her mom a bit better now. Not that she's right, but I get why she freaks out so easily.