Envy between sisters can lead to much stress. This is doubly so when said sisters share positions of power between one another. Factor in age and puberty, and the stress grows threefold.

So, what happens the younger of two siblings hits her breaking point and acts upon her urges?

Her elder shall seek retribution.

(Credit goes to both John Joseco and StreakTheFox for inspiration, and John Joseco for the image.)