The story is about a blacksmith's 18 year old daughter that has been trained to make swords and has secretly been training to fight. She is with her 2 brothers and a friend watching a fighting tournament when her younger brother falls into the arena. She jumps in and fights off a wild cat, some how with her mind after losing her sword, and saves him. She is hired by a member of royal ruling class as a weapons handler, but before she can start is sold to a slave trader by her mother, who hates and mistreats her. That’s as far as I got. I think her name was Cara.
I think you're talking about the Of Crowns and Glory series by Morgan Rice. This is the Amazon description:
17 year old Ceres, a beautiful, poor girl in the Empire city of Delos, lives the harsh and unforgiving life of a commoner. By day she delivers her father's forged weapons to the palace training grounds, and by night she secretly trains with them, yearning to be a warrior in a land where girls are forbidden to fight. With her pending sale to slavehood, she is desperate.
The name is close and it's the only thing I've found so far that's got sword forging, slavery, magic, a female protagonist, and an empire.