Yes, there are two books with the same title. While they cover much of the same information, they do so in very different ways. If you are interested in this time frame, I would recommend both.
The book by Lynda Jones is published by the National Geographic Society, and restricts itself more to the bare facts of the title characters. Both books rely heavily on Elizabeth Keckley’s autobiography, but this book also looks at the early lives of Elizabeth and of Mary Todd Lincoln, and includes photos of both women, and of some of the dresses Elizabeth created. It is a very short book, but very informative.
The novel, although it alludes to the past of Elizabeth Keckley, mostly concerns itself with the events between November of 1860, and 1901. At the beginning of the novel, Elizabeth had started a small dressmaking business in Washington City. Her skill, developed from years of making clothes for the people who owned her, before she purchased her freedom, enabled her to find clients among the Washington elite, including Mrs. Jefferson Davis. Once Lincoln is elected, her reputation allowed her to secure the position of mantua maker for the First Lady. “Mantua” was an article of women’s clothing, and by this time apparently was used as a more general term for a woman’s formal gown.
The novel describes how the relationship between Mrs. Lincoln and Elizabeth Keckley evolves during the former’s time in the White House. Having a bespoke gown created for you entailed having measurements taken, and possibly multiple fittings. If you are the First Lady, you could have your dressmaker come to you, instead of going to her. Apparently, if you were able to afford the services of a skilled dressmaker, she could also come and “dress” you before whatever event the gown was created for. That would also include styling your hair. All of this meant that Elizabeth Keckley spent a lot of time with Mrs. Lincoln, which enabled them to develop a cordial relationship. Mrs. Lincoln came to rely on Elizabeth, even after she left Washington. This may or may not have been beneficial for Elizabeth.
If this was your family, how would you research them? Very few people of that era, and even fewer people of color, published autobiographies. While our ancestors were probably not among that number, we can still learn what life was like at that time by reading the ones that were published. If your ancestor was a small business owner, they probably were listed as such in a city directory. Elizabeth’s son fought for the Union side in the war; there should be records in Fold3. If your ancestor was close to a famous person, you might find it rewarding to learn about that individual. Even if your ancestor is never mentioned, there may be things about their lives that could inform your understanding of your ancestor’s life.