The McCreas were the children of James B. and Isabelle (Cameron) McCrea. Isabelle Cameron did not have any known nieces named Maggie or Margaret Cameron. Isabelle had two known brothers; a bachelor, Allan Bruce Cameron, and A. Edward Cameron who had one child from his first marriage; an infant daughter who was born in 1892 and also died in 1892 (as did the infant's mother). A. Edward later married in 1898 and had two sons.
United States Census, 1910
Name: Maggie Cameron
Relationship to Head of Household: Cousin
Residence: Higgins, Roscommon, Michigan
Marital Status: Single
Race : White
Father's Birthplace: Michigan
Mother's Birthplace: Canada English
Family Number: 180
Page Number: 15
Household Gender Age
Duncan C Mc Crea M 25y
Adelia Mc Crea F 30y
Ellen Mc Crea F 27y
Mary Mc Crea F 21y
Jessie Mc Crea F 19y
Maggie Cameron F 19y
The assumption is that Maggie was a cousin on the Cameron side and not the McCrea side of the family (I've done enough McCrea research to make that assertion).
According to the 1910 census, Maggie's father (presumably a Cameron) was born in Michigan and her mother was born in Canada.
A search of Margaret/Maggie Camerons born ca 1891 in Michigan has not landed on a family that I recognize as mine. Perhaps I'm merely overlooking something obvious? Don't have an answer to the question of Maggie's parents.