There'd been... an incident, and one of her girls had been hurt. She'd gone after the man responsible with a pistol, shot him in the leg and then beaten him with it. Nearly killed him before they pulled her off.
Jack sought her out, knowing they'd hang her otherwise.
"You need to escape, woman. Care to become a pirate?"
She punched him hard for calling her "woman", then told him her name, Anamaria. And so the deal was struck.