Fortress of Snow by Melanie Dickerson

When her father dies and her brother, Warin, abandons her, Mazy is forced to seek help from her beloved older brother Sir John, who is training knights at the great estate of Strachleigh. While there, she becomes friends with the kind and loyal Sir Berenger. Circumstances then force them apart: Berenger goes to Prague, while Mazy and her brother move to London. There, Mazy puts her knife-throwing skills to excellent use as she defends herself, and she learns to make breads to sell in the market to earn money. Her business is expanding when Berenger returns to London and they are reunited.
Romance is just beginning to bloom when the king offers Berenger a new mission that also serves as a chance for a title: Berenger is to marry the recently widowed Lady Bristow and take over her estate. To Mazy’s dismay, Berenger agrees to go to Bristow Castle to visit her and make his decision.

But Bristow Castle is hiding secrets, and the only person who might be able to save the knight in distress is the damsel Mazy herself.