Lion of Thunder by Kathryn Le Veque

Strong women, enemies to lovers, and a little grumpy sunshine prevail!
Westley de Lohr has a secret – he’s been betrothed to the young girl who was his ‘best friend’ when he was about five years of age. Her father was a powerful neighbor and Westley’s father, seeing an opportunity, brokered a betrothal for his youngest son. As her father’s only child, she would inherit a strong fiefdom and Christopher wanted that for his son
.
But things have changed.
Elysande du Nor used to pull Westley’s hair and make his life miserable, but somehow in that childhood fighting, two fathers saw the opportunity for a betrothal. The truth was that Elysande grew up, fostered as a proper young woman, but never lost that tomboyish nature. When Westley finally shows up at her family home to claim his betrothed, Elysande realizes the boy she used to taunt has, indeed, become a man.