This is a lesbian Cinderella re-telling. 'Nough said, right?
Actually, it's probably not what you think. It's a strangely cold and bleak book in many ways. Ash spends pretty much the entire thing lost in her grief at the death of her father, deeply depressed and basically suicidal. Her Fairy Godmother is actually a twisted faerie lord called Sidhean who sort of falls for her, and her handsome Prince is the Prince's Huntress, Kaisa. Essentially magic represents a form of self-destruction, love both reality and salvation, though it is a choice Ash must make for herself.
It's not really a story about being gay as such; it's just a story about falling love. I liked that.