Life Doesn't Discriminate
Hermione was six when she spotted the door to the Leaky Cauldron and saw magic within. A curious child, she snuck through and explored Diagon Alley. Her mistake came in tripping into Knockturn Alley. When she touches a charmed ring, she's sent back to 1965 to be found by Unspeakable Alphard Black. With no way to send her back home, he adopts her and renames her Estelle Vega Black.