Each of Batman's children — adopted or directly related — has played a significant role in his life. Some of them have even carved their own paths away from Gotham, leading teams and taking on new heroic mantles. All of them are great in their own right, but some of them are more trained and accomplished while others still have some growing to do.
Cassandra Cain first appeared in 1999 in Batman #567 by Kelley Puckett, Damion Scott, John Floyd, Gregory Wright, and Todd Klein. She would soon become Batgirl and a big part of many Batman stories, including the No Man's Land storyline. One of the best fighters in the DC Universe, Cassandra surpassed even Batman.
Cassandra went up against some of the most infamous killers in continuity. She's bested her mother, Lady Shiva, and fought Deathstroke and David Cain. With her heritage, she faced a similar dilemma as Damian, but she overcame her struggles and became a valued member of the Bat Family.