Carrie's the wife of Benjamin Pitezel, trusted confidant of Holmes. When her husband is found dead, she's unable to identify the body so sends her daughter Alice to the coroner's office instead (uh, thanks, Mom?).
Holmes persuades Carrie to allow three of her children to travel with him. She believes the kids are roaming about in London under the care of Minnie Williams. But what ends up happening is Holmes is keeping them cooped up in hotels throughout the Midwest. And the worst part is: Carrie has no idea she's staying in hotels just a few blocks away from her kiddos.