Spinning Silver by Naomi Novik, 466 pages

Miryem is the daughter and granddaughter of moneylenders... but her father isn't a very good one. Free to lend and reluctant to collect, he has loaned out most of his wife's dowry and left the family on the edge of poverty--until Miryem steps in. Hardening her heart against her fellow villagers' pleas, she sets out to collect what is owed--and finds herself more than up to the task. When her grandfather loans her a pouch of silver pennies, she brings it back full of gold.

But having the reputation of being able to change silver to gold can be more trouble than it's worth--especially when her fate becomes tangled with the cold creatures that haunt the wood, and whose king has learned of her reputation and wants to exploit it for reasons Miryem cannot understand.