Everyone though poor little Belle, so afraid and alone! One of many sisters who was picked on all the time, yet none ever suspected that she was the source of their misfortunes and as such left as payment for a huge scary beast. Poor, poor Belle.
But Belle as sweet and innocent as she seemed on the outside was more of a monster then the Beast she was left for. As fair and as timid as she seemed on the outside, her soul was a dark and twisted thing. Gaining his trust and envying all that he possessed she fell in love with his golden fur.
So on the night of their wedding she poisoned the Beast as not to harm his fur and took it for herself. That and all the land and riches he had possessed.