Janette Oke 
Bluebird and the Sparrow (Women of the West Book #10) 

Sometimes she wished she was an only child . . ."She’s lovely! Look at those curls. Those blue eyes. She’s just beautiful!"Berta was used to hearing comments like that. But they were not about her. . . . Whenever ladies came to the house or met her mother on the street, they exclaimed over Berta’s little sister, Glenna.Somewhere along the way, Berta decided that whatever Glenna was, she would not be. Whatever Glenna did, she would not do. Whatever Glenna liked, she would not like. She would be the opposite.Sure enough, Glenna is sparkling, vivacious, outgoing, and adored, while Berta is serious, dependable, and prim. Their relationship grows more and more distant until, finally, Berta must look into her heart and discover what truly has caused the rift between them.