Sewell wrote and illustrated a timeless picture book of farm animals for children entitled Blue Barns. In addition to illustrating the Wilder books, some of which were co-illustrated by Mildred Boyle, Sewell illustrated books by Elizabeth Coatsworth, Eleanor Farjeon, Frances Clarke Sayers, and many others.
The Sewell-illustrated editions of the "Little House" books went out of print in 1953, when Harper & Brothers (now HarperCollins Publishers) released the uniform edition of the books illustrated by Garth Williams.
Helen Sewell died in 1957 at the age of 61.