These books, by 20th century women writers, are each about the art of writing. They'd make an interesting series for a reading group. Individual readers may also find them useful and, perhaps, inspirational, in their insights into the lives of women writers.
1. Writing for Your Life : A Guide and Companion to the Inner Worlds
by Deena Metzger
2. How to Suppress Women's Writing
by Joanna Russ3. The Writing Life
by Annie Dillard4. Dancing at the Edge of the World : Thoughts on Words, Women, Places
by Ursula K. Le Guin5. Man-Made Language
by Dale Spender