He shows her mercy

Boba said to the crying girl, "none of this would happen if you didn't disrespect me." She begged, "I'm sorry, Lord Fett! Please let me live." "That's more like it," Fennec Shand was pleased by how swiftly her boss crushed any challenges to his rule and made his enemies submit.

Boba spared her life, "I'm not an unreasonable man. You may live. But burn this night to your memory so you never forget what happens when Boba Fett is disrespected!" Word will spread of this night and all of Tatooine will submit to him or be disintegrated.