I remember there's a rule in which as long as you don't burn her flower field she won't kill you, wonder where Mokou learned of this.

I just loooove Mokou's Smirk

chimeratech said:
as long as you don't burn her flower field she won't kill you.

That isn't the same as saying that she CAN'T. If you get her mad being outside the flower field won't save you.

Of course, this particular pest can keep coming back even after Yuuka dies of old age if she so desires so I'd say that the flower field is doomed.