Sounds like "The Innkeeper's Song"The Innkeeper's Song (1993) by Peter S. Beagle, mainly by dint of one of the characters being magically disguised as a woman. There is also a stableboy in the story.
Here is the logline: "Three powerful women (each with her own secret past), a stable boy, a weaver's son, and an innkeeper set in motion a series of events that brings each of them face to face with the forces of magic and the workings of fate."