You were Harry's sister and today someone gave you a drink but you didn't know it was a potion to make you got back to when you were a little kid, you were 16 years old like the Weasley Twins, Fred and George, and they laughed and tease you because you were in your 3 years old self.

But then you begged them for them to help you and they accepted because you were their bestfriend so they took you to their dorm and when they cast a spell you told them to close their eyes, that's what they did, you were in your normal body now, your 16 years old body.

And you hide behind a curtain because you were n3ked, and Fred and George opened their eyes, they only see your head and not your body because you're hiding, back in your normal body.