Alright, so since I haven't looked at the next page yet, I'm actually going to guess what she said/says just for the heck of it. My guess is going along the lines of either "So we don't constantly kill each other" or "so that things are fair."
Time to go see how wrong I am!
Why does everyone fight with spellcards? I asked my big sister that long ago.
And what do you think she said?