"The way they have expressed grief with the words and illustrations is incredibly moving and it is an uplifting book. I think it will be a wonderful thing for anyone who has lost a family member to cancer - especially someone young."
Rodler said the book's title was a quote from one of the children in the family when his aunty had lost her hair after chemotherapy treatment.
"I talked about it with Frances and we decided it would be a wonderful line for a children's book."
Both the book's collaborators had to come to terms with their own grief while working on the book.
"I wanted to incorporate things of Leah's - photos, the colours she loved, things she wore, things she made," Wilkinson-Smith said.
"I decided the illustrations would need to be collages but every time I began, I would start crying. Once I finally assembled everything I needed I could work without crying and it came together."
The book also serves as a means for readers of all ages to find their own qualities and strengths by thinking about what is under their own hats and Wilkinson-Smith has included "treasure hunt" pages at the end of the book.
Leah Te Weehi, of Tuhoe and Ngati Porou descent, was awarded the ProCare Prize in General Practice as a fifth-year undergraduate at the University of Auckland School of Medicine in 2010.
She put her prize money towards a study placement in London and travel was one of her life's passions which have been expressed in the text and illustrations of What's Under the Hat Aunty?
"It's a picture book which lifts the reader above the sadness, and I love the slant they have given the book," Stead said.
Copies of the book along with originals of Wilkinson-Smith's illustrations are for sale at the Lockett Gallery, 60-62 Guyton St and all proceeds will be donated to the Child Cancer Foundation.