Two Different Souls (one direction fan fic/Nialls hidden sister)

What if you were related to one part of the biggest boy bands in the world? No one knows about you because you aren't on very good terms with each other, but it is only because of assumptions. He assumes you're anorexic, while in all reality you aren't, you have IBS. You assume he wouldn't be interested or care, when he always has and always will. One day Darcy Fiona Horan is forced to go on tour with her brother and his band mates. What will happen?