Blade of Secrets by Tricia Levenseller

Eighteen-year-old Ziva prefers metal to people. She spends her days tucked away in her forge, safe from society and the anxiety it causes her, using her magical gift to craft unique weapons imbued with power.

Then Ziva receives a commission from a powerful warlord, and the result is a sword capable of stealing its victims' secrets. A sword that can cut far deeper than the length of its blade. A sword with the strength to topple kingdoms. When Ziva learns of the warlord’s intentions to use the weapon to enslave all the world under her rule, she takes her sister and flees.

Joined by a distractingly handsome mercenary and a young scholar with extensive knowledge of the world's known magics, Ziva and her sister set out on a quest to keep the sword safe until they can find a worthy wielder or a way to destroy it entirely