Carrie Kelly was featured in Frank Miller's The Dark Knight Returns and the follow-up The Dark Knight Strikes Again. As a young girl, she's inspired by Batman coming out of retirement, and decides to join him. She saves up some money to get a costume, grabs a slingshot, and seeks out Batman. She is able to help him out in a fight he nearly loses, and carry him into the Batmobile so that Alfred can attend to his wounds. Despite the fact that Batman is still scarred by the death of Jason Todd, he accepts her as Robin.
In the sequel, Carrie ditched the Robin costume and became Catgirl, wearing a leopard print catsuit and roller skates. She had become Batman's most trusted ally and commander an army of Batboys (who I believe were the Sons of Batman from the first book, but I haven't read the sequel in forever).
Pros: The green glasses and the slingshot make for (I think) the coolest Robin design.
Cons: Having a 13 year old girl running around as Robin (or a 16 year old as Catgirl) is probably not a good idea for a major movie, and in a realistic-ish environment, it would be awfully irresponsible for Batman to let Carrie fight alongside him. And of course if there's going to be a Robin, many people would be upset if it wasn't Dick Grayson, or if Batman's going to have a lady sidekick, they'd want Gordon.
How I'd do it: The DKR setup was that Carrie was saved by Batman on his first night back from retirement, and though her parents were still alive, they were so neglectful that they didn't notice she was sneaking out at night. I guess if you're going to include her, that's the way to go.
Casting Guesses: I don't know enough kid actresses to take a guess at this one. I heard someone suggest Ellen Page, but I think you need to go younger.
Verdict: Nah, but she is prety awesome. At least in the first book, and if you're a Batman fan you should totally read that.
After The Scarecrow, Ra's Al Ghul, The Joker, and Two-Face, who should be Batman's next enemy in the Batman Begins/The Dark Knight series? Well, as of now we know that Tom Hardy will play Bane and Anne Hathaway will play Catwoman.
Check out the master list for all the villains covered. I've pretty much run out by now. Obviously, there are more Batman villains, but not any of significance that I know of. As of February 2009, no one is confirmed as a villain. Not the Johnny Depp Riddler, not Phillip Seymour Hoffman Penguin, nobody.