In the Time of the Dragon Moon by Janet Lee Carey

A girl living on the outskirts of a kingdom with a father of considerable healing talents.

The Queen wants a second child. She has a healing man and his daughter,Uma, kidnapped so that they may cure her barreness by the time of the Dragon Moon.

When her father dies this task falls to Uma.  If she fails she will be burned at the stake.  The danger increases with the murder of one of the royal Pendragon line.  Uma turns to the king’s nephew as an ally.  But can they stop the plot to overthrow the Pendragon throne before it is to late?