Who is Cathy from Willow and what is their importance?

Cathy is David's wife and Willow's sister-in-law. Cathy is a kind woman who does her best to make Willow feel at home when she moves in, including buying her watercolor paints in case Willow should like to cope with her emotions through art. When Cathy learns that Willow wishes she could baby-sit Isabelle, Cathy's daughter, Cathy entrusts Willow with the baby while she runs errands even though there is doubt as to whether Willow is emotionally ready for the task.