Hogwarts

On the night Voldemort attacked the Potter home in Godric's Hollow, there were two children in the house: one-year-old Harry and his younger sister, who was not yet a month old.
After the deaths of James and Lily, the wizarding world celebrated the fall of the Dark Lord, but only a few knew that Harry had a sister. To protect the girl from the remaining Death Eaters, her existence was kept secret. Harry was sent to the Dursleys, and the girl was placed with a wizarding family under the care of her old friends, the Potters.
So the brother and sister grew up without even knowing about each other.
At eleven, Harry received a letter from Hogwarts and found himself in Gryffindor. There, he befriended Ron and Hermione, became the youngest Seeker in a century, uncovered the secret of the Philosopher's Stone, and helped stop Voldemort's return.
A year later, new first years arrived at Hogwarts.
Among them was a girl with long reddish-brown hair and brown eyes. Physically, she was almost an exact replica of Lily Potter: the same soft features, kind smile, and easy grace. From James, she inherited his brown eyes, unruly hair, and a bit of his stubbornness.
During the distribution, the Hat almost immediately shouted out:

• GRYFFINDOR!
  The faculty table burst into applause.
  When the girl sat down at the table, many students exchanged surprised glances. The older students, who had seen old photographs of Harry's parents, couldn't shake the feeling that they were seeing a young Lily Potter standing before them again.
  Harry himself also noticed something familiar in her appearance, but he couldn’t understand what exactly.
  Only Headmaster Dumbledore knew the truth. Sometimes he'd watch the brother and sister sit side by side, unaware they were family.
  And Hogwarts seemed to sense it: moving staircases constantly pushed them together in the corridors, and the teachers couldn't help but think of Lily every time they saw a new student.
  No one yet knew that the ancient castle held one of the Potter family's biggest secrets—the secret that the Boy Who Lived was never his parents' only child.