And so we have a scene between the two princesses. The king's daughter does something nasty to her cousin, and shifts blame so that the cousin gets blamed for doing something nasty to the king's daughter.
Note the great precision that I use to define the scene. I need something -- not too dreadful, because it wouldn't fit the fairy tale tone -- and fitting both the somewhat spiteful king's daughter and the quiet and retiring cousin (who has, BTW, a magical ability to control rose bushes).
The things that stymie you.