Who is Margarethe Fisher van den Meer from Confessions of an Ugly Stepsister and what is their importance?

Margarethe is never content with her lot in life. She always aspires to more. Her supposed motivation for such aspirations is her daughters, but one suspects she has more selfish bearings to propel her search for money and power. People believe her to be a witch. She was brought to England by her father and married an Englishman named Jack Fisher. When a flood ruined the village's crop, Jack was blamed and according to Margarethe, murdered. She fled with her two daughters to find her grandfather in Holland.