Bertha Marilla "Rilla" Blythe was the youngest of Anne (nee Shirley) and Gilbert Blythe's six children. She was named for Anne's two mother figures: Bertha Shirley (nee Willis), her birth mother, and Marilla Cuthbert, Anne's adoptive "mother". Rilla has five elder siblings - Jem, Walter, Nan, Diana (or Di) and Shirley Blythe.
Rilla is described as a "roly-poly plump" baby in the first two books she appears in (Anne of Ingleside and Rainbow Valley), with fiery red hair that is darker than the "carrots" colour but not quite auburn, which she inherits from her mother, Anne Blythe. Rilla has the hazel eyes of her father Gilbert.
At the beginning of the book, Rilla of Ingleside, in which she is featured as the main character, she is fourteen, very vain and quite spoiled. Her brother Jem and old playmate Jerry Meredith leave to fight soon after it is announced that England has declared war on Germany, and her whole world is turned upside down.