Who was mrs Cunningham in the book cheaper by dozen?

In the book "Cheaper by the Dozen," written by Frank Bunker Gilbreth Jr. and Ernestine Gilbreth Carey, Mrs. Cunningham is not a character.

The book is a memoir about the authors' childhood experiences growing up in a large family with 12 children. The story primarily revolves around their parents, Frank Bunker Gilbreth Sr. and Lillian Moller Gilbreth, who were pioneering industrial engineers and the "parents" of the dozen children.

It's possible you are thinking of a different adaptation of the story, such as the film versions, which might have introduced the character of Mrs. Cunningham.