I have to admit I'm glad the A-Z Challenge is winding down. Even though I scheduled these posts well in advance, it's been a lot of work putting them up and adding links and pictures. I only have one woman listed for Y, Jane Yolen. If you're familiar with her work, I'm sure you'll agree she's a good choice. Yolen has written poetry and nonfiction, but she's best known for her children's books. (I did read some of the How Do Dinosaurs...books to my son when he was a toddler.) She's won the World Fantasy Award for Life Achievement, and her work has been nominated several times for the World Fantasy Award. I particularly enjoyed Sister Light, Sister Dark and White Jenna. You can learn more about her on her website and Wikipedia and find her books on Amazon.
Please feel free to name more Y SF/fantasy women authors in the comments below.