Maisabelle,
Sorry to hear about your loss, but what your other daughter did is very thoughtful. And I agree that the meaning of such tattoos is for the person who wears them.
Rock cairns are used in the woods as trail markers to guide the way for hikers. They remain balanced in the worst of weather, and it will remind me to stay balanced in my life, as well as to trust the direction that certain scenarios in my life may take me.