Great profile of Peggy Rathmann at SFGate.com.
Rathmann spends at least nine months on each book she writes and illustrates. Before she even begins a book, she might make clay models of characters or get her nieces and nephews to pose as possible characters, which she'll photograph for ideas. Although she might bang out a story in just a few weeks, the story and the illustrations go through numerous revisions. As the pictures change, lines in the story may, too.