Selina was working in a burlesque club when it was raided by Batman due to Mafia workers frequenting it. She respected this terror inducing appearance, and was glad he took down the men responsible for the shady business. It turned out she was stealing from them anyway, so having them get put behind bars helped her elude punishment.
Selina has 4 cats in her private flat, Shmeez, Cow, Sassy and Ron (a rare Calico male). She feeds at least six more neighborhood cats and lets them come and go as they please.
Even though she has been an enemy of the Batfamily, she always had a soft spot for them, and their father, Bruce. They understand each other, and often let Selina go, when they should take her down. She never takes this for granted, and doesn’t tease them for it - even going as far as to help them out in similar situations.
Selina is closest to Dick Grayson having known him since he was nine.
Despite being very capable with a gun, Selina personally hates them. Her father got into a bar fight with a very powerful member of the Mafia, and used a gun, which ended up shooting his wife hospitalizing her, and ultimately led to her death.
Like the Batfamily, especially Bruce, she has a strict no killing policy, this is due to her childhood trauma as well as Bruce’s influence on her.
Selina has a sister however she has long since lost contact with her. Last she and her sister spoke she was working in one of Roman Sionis’ many businesses. On occasion, Selina will visit her sister’s apartment, and watch from a distance, making sure she is well kept.
Bruce and Selina had an off and on relationship, however they parted ways romantically when they both realized their work was more important. They remain friendly, and Selina doesn’t know about his new lover.
Selina keeps herself to a pretty private life, but has a few people she considers her really good friends: Harley Quinn, Ted Grant, Bruce Wayne, and Kitrina Falcone.