She and most of her coven were executed by the Volturi for "attracting" too much notice from humans.
Anne had a younger sister named Victoria, but she could not go back for her until she was strong enough to control her bloodlust. Once she became strong enough, Hilda gave her permission to go looking for her sister. She was thrilled when Victoria joined them. They lived happy lives, and 2 years later, Hilda added Noela to the coven shortly before the Volturi came and accused them of drawing too much attention to themselves. Hilda immediately came to defend her coven and allowed Aro to read her mind to prove them wrong; however, he still confirmed that they were criminals and Hilda was immediately executed, though she tried to argue.
Her existence was only mentioned in The Twilight Saga: The Official Illustrated Guide.