Up to date for those who know jacksquat on the comics. This is the 3rd Batgirl, Barbara Gordon was 2nd and then there was Batwoman's Sidekick (whose name leaves me right now but she has/had a new handle of Flamebird I think) from way back when (wore dresses they both did and then I think went to Spandex. Her outfit was red & green)
Cassandra Cain was the only one to get her own actual series where as Babs, who retired and is now Oracle computer wiz to the Heroes.
Babs in the books was having an evening at home with her dad Commisioner Gordon when a knock came from the door. She answered and met a bullet that ruptured her spine and paralized her from the waist down. YOu can thank the Joker for this cause its one of the big things he did to make him the #1 Villian of all time. Think the story is "The Killing Joke" if I remember right, could be wrong. But it was a prestige format book if I recall right. (Zero Hour introduced us to a Babs who didn't get shot but James Gordon did but she DIES at the end of the series. Also we could say Zero Hour is the first time we see Harley Quinn but not of Earth 1 (she was in green and black))
Cassie is the daughter of a killer named Cain and Lady Shiva. She was at first mute and eventually learned to talk but she kicked ass and for those folk who hated her costume, she tried on Babs, hated it cause of the heels and I think from there for anybody seeing Terry Dodson art of a "Batgirl" from comics fighting the 3rd it's not Babs it's Harley Quinn who STOLE the outfit and paraded around Gotham in it. (later Poison Ivy donned it and the suit had to be destroyed cause her sweat could kill yah.)
There is no more Batgirl in DC now. Cassie was killed, Babs is still wheelchair bound, and well already mentioned Flamebird (the 1st Batgirl). Though CAssie was revived thanks to a Lazuras pit and then killed her mother at the end of the series. She recently showed up again in Robin and well now if what I saw in a preview is correct is now an Orphan at her own hands.