The Poisoner's Enemy (a Kingfountain prequel) (The Kingfountain Series)
From Wall Street Journal bestselling author Jeff Wheeler:

Before she befriended a frightened young boy in the palace of Kingfountain, Ankarette Tryneowy grew up during the shattering civil war that raged between members of the Argentine family. This is the story of how the only daughter of a lawyer and a midwife became the famed Queen’s Poisoner.

Recruited by King Eredur’s ambitious uncle, Ankarette is thrown into a world of double dealing, deception, and tangled loyalties. With the help of her mentor and friend, Sir Thomas, she must learn to trust her instincts and remember that others will not always be loyal, even when they are of the same blood. But involving herself in the machinations of the realm draws the eye of an enemy more dangerous than kings or dukes. How will she navigate the politics of the realm and the desires of her heart to become the woman she needs to become?