A librarian asked me to recommend a few science fiction novels for women who haven’t read any science fiction. I replied:
First and foremost, if possible, you want the main protagonist to be female. And unless the reader happens to love science, you don’t want hard science fiction, you want soft: anthropology, sociology, psychology, ecology, and so on.
The first choice, that fits all the criteria above:
Sheri S. Tepper’s Grass.
If the woman reader has interests in certain areas, you might want to build on those interests.
For a woman who is interested in history, or who cares about slavery in general or U.S. African American slave history in particular:
Octavia Butler’s Kindred.
For a woman who enjoys a romance intertwined with politics:
Catharine Asaro’s Primary Inversion.
I’d recommend one of those three, with Tepper being my main choice.
If you want a few more suggestions, I’ll break the female-main-protagonist rule.
If the woman is strongly interested in psychology, particularly in autism:
Elizabeth Moon’s The Speed of Dark.
If the woman loves a challenge and has strong literary leanings (loves prose that sings and layers of allusion), can tolerate ambiguity and initial reader confusion, has a taste for the strange, and is interested in gender issues:
Ursula K. Le Guin’s The Left Hand of Darkness.
(But be careful if you recommend Le Guin! Novice science fiction readers have to work before they feel comfortable with the book.)
Returning to the female-main-protagonist rule, if the woman is interested in gender issues but doesn’t love a challenge as much as I’ve described above, then intead of Le Guin:
Joan Slonczewski’s A Door into Ocean.
Kage Baker. Sky Coyote.
Lois McMaster Bujold. The Warrior’s Apprentice.
Daniel Keyes. Flowers for Algernon. (the 1966 full novel, not the 1959 short novelette)