It's a series of books, I believe written by a British author, about a young woman searching for her identity. It starts with her working as a shunned maid in a tower where they train flying horses (or wyverns) for battle. The woods surrounding the tower are dangerous, filled with malevolent creatures (heavily inspired by Celtic / Scottish mythology). She escapes on one flying creatures, goes on various adventures throughout the series, ends up getting her face restored, marrying the king. King turns out to have been the elf king, forgotten by humans when the rest of his race went into another universe. She turns out to have been one of the humans chosen to go with the elves to the other universe. The series ends with him going back and her staying here. A bittersweet ending, the entire series is a bit a dark note, but very well-written and original (despite the use of elves).
I've tried for quite some time, but I am unable to recall the name of the author or the name of the book. In fact I can't remember the name of kany characters either. It's been a long time.