I love her illustrations for children's picture books such as Sylvia and the Bird and Augustus and His Smile, both of which she also wrote. They are so free and distinctive, and blissfully uncartoony in comparison to many modern children's illustrations. There's an element of wonder or even (dare I say it) magic suffused through the quality of the images that I find refreshing. They're quite impressionistic, in their own way, which I like a lot. We don't necessarily have to simplify things for children.
Below are a few of her illustrations, more of which you can see over at her official website.