She preferred to write 'under a pseudonym'. [=using a false name instead of her real name]
Mark Twain is the 'pseudonym' of the American writer Samuel L. Clemens.
a 'pseudonymous' author
(..) What? Evelyn Waugh was a man. Oh, come on. She's nice. What? You know... You know, not everybody went to Yale. It was just a pseudonym, for Christ's sake. Why do you have to defend her? Well, why do you have to point out how stupid everybody is all the time? I thought it was funny. Forget it. (..)2003 Lost in Translation