I liked the flow of the narrative within the poem, though I thought having her rival be her sister seemed almost contrived (unless this is a true story). This reads too real to almost hurt. :)
Author's response
I don't quite understand your last sentance.....
This isn't based off a true story, though. I had to write a narrative poem for my Creative Writing class (which was amazing, by the way) and the image of two people dancing on the beach came to my mind. I thought about making them best friends, but it would have been harder to show it and have it still be a poem.