Mary J. Blige related closely to her character, as she had an Aunt who embodied her character Florence, who had worked for and raised a bunch of kids in a white family who loved her. Additionally, she saw her character also in the experiences of her grandmother.
Director Dee Rees shared photographs from the film's era with Carey Mulligan as part of her preparation, and she was drawn to a particular one of a woman with a really short fringe (bangs) who looked so awkward to her, which she thought reflected her character Laura. Thus, she cut her hair in a similar style for the film.
"Mighty River" marks Mary J. Blige's third original song written for a motion picture. She co-wrote it with Raphael Saadiq and Taura Stinson. Her other motion picture contributions include "I Can See in Color" (from "Precious: Based On The Novel "Push" By Sapphire") and "The Living Proof" (from "The Help") for which she received a Golden Globe nomination for the latter.