Penn-Lewis reportedly struggled with an unspecified lung disease throughout her public career, and at times had to cease traveling or speaking in order to recuperate. It has been speculated by her biographers that this mysterious disease was tuberculosis. She described her health problems as a "baptism of suffering". Her repeated recoveries reinforced in Penn-Lewis the belief that her God wanted her to continue with her ministry. She wrote books, such as "Thy Hidden Ones: Studies in the Song of Solomon" and " The Story of Job", while recuperating.