Prolific female author. Anonymous has written hundreds of thousands of books,
articles,
poems, essays, memos,
broadsides, and
treatises.
Seriously, though, under this name, many women for centuries have written, published, or produced art, either deliberately to avoid the problems and punishments awaiting the woman artist, or by default because their names were lost or forgotten.
Pen names, used by women to protect their anonymity for a variety of reasons, often add to their invisibility; Deborah Rosenfeld counted 25 pages in the British Museum Catalouge headed simply "A Lady" and an 1880 pamphlet lists 151 works by English writers published under that name.