The Question and Answer section for Girl With a Pearl Earring is a great resource to ask questions, find answers, and discuss the novel.
Cornelia does not like Griet's presence in their home. She does not like the relationship she perceives between Griet and her father, and thus, sets about trying get Griet into trouble and thrown out of their home. Cornelia steals items and plants...
Catharina will not allow Griet to visit her family because there has been an outbreak of plague. She forbids Griet to visit them until after the threat of contamination has passed.
I can't find this exact quote. What chapter are you referring to?