A.U. Harry Potter's Little Sister

In an alternate universe, Harry James Potter has a younger sister named Lillianae Alice Potter, who is a year younger than him. While Harry is known for his bravery and direct approach to problems, his sister is more mysterious and keeps to the shadows. Little is known about her, except that she, like Harry, was sent to live with the Dursleys. While Harry was off enjoying his time at Hogwarts, his sister was trapped at the Dursleys' home. She learned from the previous year's experience and opened her Hogwarts letter in the hall, knowing how the Dursleys would react. After that, she retreated to her and Harry's shared room, alone. When Harry was rescued by his Hogwarts friends using a flying car, there wasn't enough room for his sister, so she was left behind.
While at Hogwarts she becomes close with one Draco Malfoy.... How will things end?