The main occurrence of sexual abuse in The Immortal Life of Henrietta Lacks occurs after Henrietta's death from cervical cancer, which results in her children being placed in the care of Ethel and Galen, a couple who was acquainted with the Lacks family and who took advantage of the children in horrific ways.
The book describes how Henrietta's daughter Deborah was sexually abused by Galen, who was violating his role as a parental figure, and how nothing was done to stop this horrific treatment:
She tried to tell Day when Galen touched her in ways she didn't think he was supposed to, but Day never believed her. And Ethel just called Deborah words she’d never heard, like bitch and slut. In the car with Day driving and Ethel in the passenger seat, and everybody drinking except her, Deborah would sit in the back pressed against the car door to get as far away from Galen as she could. But he’d just slide closer. As Day drove with his arm around Ethel in the front, Galen would grab Deborah in the back seat, forcing his hands under her shirt, in her pants, between her legs. After the first time he touched her, Deborah swore she’d never wear another pair of jeans with snaps instead of zippers again, but zippers didn't stop him; neither did tight belts. So Deborah would just stare out the window, praying for Day to drive faster as she pushed Galen’s hands away again and again.
As the previous educator who answered this question has mentioned, the book does not directly reference Henrietta being sexually abused. However, the fact that Henrietta and Day were cousins and grew up sharing a room together—which certainly led to her impregnation and the birth of her first child when Henrietta was merely fourteen years-old—also indicates that things were significantly awry with Henrietta's home life. Henrietta was certainly younger than the age of consent; could this have been forced sexual conduct? The book declines to say, and yet, from the impression we get of Day throughout the narrative, we can certainly draw our own conclusions.