Dr. Harding was one of two women imprisoned by the Japanese at Cotabato in Biggles in Borneo. An American doctor specialising in tropical diseases, she was kept in a house on the hillside, separate from the male prisoners who were kept in the local civil prison.
During Biggles' raid on Cotabato, Harding and the other woman prisoner, Mary Stockton, was rescued by Jackson. The two women were taken to Lucky Strike on board the Cayman and then ferried to Australia by the Liberator. Not much is made of her medical specialty. She might have been useful treating the injured at Lucky Strike, for example, but she played essentially a passive role in the plot and doesn't even get a line of dialogue.