Why is volunteer work during the war not a good choice for Penelope?

After volunteering for the war, she is assigned to the Wrens. As she has little skill and qualifications deemed important by war officials, she is given a low-grade title as Steward and told how to wear her hair and dress. For Penelope, with her bohemian lifestyle and free-minded parents, this is an entirely new way of seeing the world and living. She is instantly depressed and questions why she volunteered to begin with.