1987’s Arrows of the Queen is the first volume in a Mercedes Lackey series, the Heralds of Valdemar.
At thirteen, Talia faces an arranged marriage. Whether she will be some stranger’s Firstwife or an Underwife matters little to Talia, who has no interest in being an overworked brood mare. Talia also has no interest in entering the Temple Cloisters as a silent servant of the gods. Since those are the only two choices the patriarchal Holderfolk offer women, Talia seems doomed to a miserable life.
Fate intervenes, in the form of a magical telepathic horse.