Eloise Lorelei Lupin was the twin sister of none other than Remus John Lupin; when they were both very young Greyback decided to get revenge on the poor twins' father and meant to kill them both. However, he didn't succeed and only managed to bit them. Eloise and Remus became werewolves from that night and, once they were 11, they both got their Hogwarts letter.