You just used your ability you know

Then, what should you all do? This way that child has lost her qualification

and of course, the [I won't use my ability] lie can't be used as Melling already used it

If she ended up killing me, she would have been disqualified. However, that knife was going to stab me without hesitation.

She knew long ago that when I am in danger, Cirno will indefinitely try to save me