Harry Potter: Professor, I'm Harry's Big Sis

The heroine is Millie Potter, Harry Potter's twin little sister.

She grew up with her maternal grandparents, the Evanses, very close to Spinner's End.

As a child, she was a little devil, climbing onto the roofs and tearing up tiles. The roofs she climbed were in Spinner's End, and the tiles she tore up were from Spinner's End.

As she grew up, she became Lily's spitting image, except for her eyes... Just kidding, even her eyes looked like Lily's. She's in the same year as her brother and is also in Gryffindor.

Grateful that Snape never held her childhood rooftop escapades against her, she stands by him unconditionally. She even argues with her brother before Potions Class:

“I think Professor Snape is great! You can't pick on him just because he's a little ugly!”

Snape, walking into the classroom: Thanks, I guess...

Snape couldn't believe that this little face, identical to Lily Evans's, had somehow acquired a venomous tongue just like his own.