Erin was born in a normal non-wizarding family and the idea of her being a witch never occurred to her. Even the slightest proof that she could sometimes make things move with her own mind wasn't a clue. She thought it was normal and Kristina as her sister was unlucky enough to missed the opportunity of having one. When she entered Hogwarts, Erin was pretty convinced that she's a Muggleborn who never had an inclination to any wizards. But, life was pretty harsh for she found out that she was only adopted and actually came from a Pureblooded wizarding family.