Journey into Darkness (Book 3 in a trilogy)

Kit Markham decides to leave her family in Melbourne and takes a fast clipper to England. In London she answers a call for help and volunteers to work on a hospital ship bringing back the wounded from the Crimean War. From this experience she sets herself the goal of training to become a doctor. She travels to America and, despite setbacks and delays, she achieves her goal.
She falls in love and marries her supervising doctor, Ned, and they have a child but the life they envisaged is shattered by the outbreak of the Civil War. The Union Army refuses to recognise her services as a doctor but she obstinately remains working in the battlefields beside Ned. At Fredericksburg, she is captured by rebel soldiers and becomes a prisoner-of-war.