H stands for "Help! There are too many great authors under this letter!"
Nina Kiriki Hoffman is an award-winning (Nebula, Bram Stoker, plus nominated multiple times for the World Fantasy Award and several other awards) SF, fantasy, and horror novels. Her style reminds me a bit of Patricia McKillip. I've read a few of her works, such as The Thread that Binds the Bones, The Silent Strength of Stones, and A Red Heart of Memories. Learn more about Hoffman on Wikipedia and Amazon.
I discovered M.C.A. Hogarth through her Kickstarter for Black Blossom. The concept intrigued me enough to make me back it, and I wasn't disappointed. Since then, I've gone on to enjoy other stories of her, particularly those set in the Pelted Universe. (It features genetically engineered animal-human hybrids who colonize space.) She's a hybrid author and artist, and she recently helped persuade SWFA to open its doors to indie authors. I don't qualify (yet), but I would definitely support her for SWFA office. Learn more about Hogarth on her website, Wikipedia, and Amazon.
Nalo Hopkinson has won the John W. Campbell Award for best new writer, The Locus Award, the World Fantasy Award, and others. She was a Guest of Honor at WisCon in 2002, and if my memory serves me correctly, I was part of her group for the writers' workshop that year. Learn more about her and her work at her website, Wikipedia, and Amazon.
I discovered Tanya Huff through her Blood books, which features a vampire paired with a detective. I've read some of her other series too, such as the Wizard Crystal and Enchantment Emporium series. Learn more about her on Wikipedia and Amazon.
Honorable Mention: Sarah Hoyt (blog, Wikipedia, Amazon)
How many other SF women authors with "H" names can you add to this list?