Police say they are investigating the death of the unidentified woman as a homicide following the fire Monday morning in Lancaster.
Police say two girls, ages 8 and 9, were hospitalized in critical condition. A man and a teenage boy who were also in the house when the fire broke out were treated and released.
Investigators say they believe the blaze was not a random act but declined further comment. An autopsy to determine the woman's cause of death is scheduled for Tuesday.
Fire officials say two of the children were rescued from the home's roof by a neighbor.