Patricia A. McKillip 
In the Forests of Serre [EPUB ebook] 

Everyone in the kingdom of Serre avoids the Mother of All Witches, an ugly, powerful and dangerous woman who lives in the forest. When the Prince of Serre, blinded by grief at the death of his wife and their newborn, rides down the witch’s white hen, he earns her curse. Prince Ronan believes nothing can be worse than what he has already experienced, but he soon discovers that he is wrong. The curse of the witch in the Forest of Serre has only begun to exert its baleful influence…