The Twin Sister

Harry Potter has a twin sister, but she isn't completely normal. Her adoptive father is Sirius Black. Godfathers are Severus Snape and Remus Lupin. What happens when the only friend she's ever had betrays her? Who will she choose: Sirius (her father) or Harry (her brother). This is a bad summary, sorry. Rated T because I wasn't sure what to label it as. (more based off of movies)