Believe it or not, Selina Kyle aka Catwoman has a sister...who's a nun!
Maggie Kyle is the younger sister of Selina Kyle, the Catwoman. Unlike her villainous sister, Maggie is a nun. She eventually left the convent. Maggie's relationship with Selina grew distant as they got older. She eventually left to find a new life and explore the world. Moving to the West Coast, she met her future husband, Simon Burton. Years later, Simon's work transferred them to Gotham City, where Maggie reunited with her long lost sister, Selina.
The reunion was short lived though when she and her husband Simon were kidnapped by Black Mask all in an effort to hurt/get to Catwoman. Though she was rescued by Selina, it was too late. She had been tortured and forced to eat her husbands eyes. Simon died at the hands of Black Mask. The events caused her to snap. She was then entered into a psychiatric institute.
She remained in there for some time, before the Black Mask returned from the dead in Blackest Night, seeking revenge on Catwoman for killing him. The fear of seeing him again set Maggie to new lows and even though her sister was helping her, she blamed Selina for everything that had happened to her. As Selina and the Gotham City Sirens fought Black Mask, Maggie ran away.
Maggie believed that her sister was possessed by a demon, the sign of the demon being the cat. She sought out Sister Agatha, a tough and renowned exorcist, to help her save her sister. But in her apartment, Maggie lost control when she saw the sisters cat, killing it and attacking and possibly killing Agatha as well.
Searching her apartment, Maggie found many relics and tool of the exorcist's trade. Among the weapons and crucifixes Maggie found a vile which broke on the floor, releasing what Maggie believed to be an angel. The angel claimed it would guide her and help her destroy the demon in her sister. Donning a habit and various weapons, Maggie now sought her sister to save her soul, allowing the madness to enter her so she could combat the evil of the cat-demon.