Katarina is the illegitimate daughter of Hugh Montbarron -- the former Grand Master of the Legion -- and a Lescanzi witch. Her mother's people are nomads and wanderers, distrusted by many people in Ehb... but they are skilled in both warfare and magic, and Katarina has been trained in their ways. Unless you are using her as your main character or have unlocked her as a follower, she will be Leona's sister.If not, then she is replaced with Leona's brother.
Katarina takes a thoroughly practical approach to conflict resolution: stay out of sword's reach, and settle your problems with firearms. With her rifle in hand, she can fell distant foes, and even the most resilient enemy can be brought down by her ensorcelled bullets and debilitating curses. When forced into close combat, Katarina uses sorcery and a pair of short-range side arms to repel attackers.
Katarina is available to the player either as their main character, or after the events in Ravens Rill when the player is going to Stonebridge. She is the third easiest player to get the "Maximum Charisma" Achievement.
Katarina differs greatly from Anjali and Lucas. While playing as Katarina, it is generally advised to stay out of the way as much as possible while Anjali and/or Lucas soak up the damage as they have much higher health. Although Katarina's pistols are good, they have incredibly limited range and are only at their extreme best when an enemy is within a swords range of you.
However, one of Katarina's big strengths is her ability to hurt enemies as she diverolls and her ability to summon a Black Hound Familiar, which is far stronger than Anjali's Fire Jackal Familiar.