Why is Joy Stepaneevong alone during her time in the hospital in the novel, Operation Wandering Soul?

Joy Stepaneevong is a twelve-year-old refugee from Southeast Asia, who is hospitalized for a growth above her ankle. She is alone because her mother is dead, and her father, an illegal alien. Her father is a genuinely caring parent, but he cannot expose himself to the possibility of detection and deportation by visiting the daughter he loves.