Mira's first appearance occurs in Batman The Dark Knight 1, right in the end. While Bruce investigates Dawn's disappearance, he leaves the Batmobile outside. We can only see someone in a hood trying to hack the car.
We realize later it is a girl. The girl, scared because she listened Croc and the Penguin chatting gets in the batmobile, and then tries to drive it. At the same time that both crooks are leaving with Batman.
She fails to drive the batmobile and Alfred suddenly speaks through the comms to try and help her. The girl manages to gain control of the batmobile, while Alfred tries to reason with her and understand why she stole the car.
She replies saying she had no choice. Alfred let her know that whoever told her to steal the car won't leave her alive. The girl agrees to leave the car wherever he wants.
We learn about her name in The Dark Knight issue number 4. It is Mira. We see her arriving in her neighborhood just in time to witness two thugs attacking a man that was supposed to pay them an huge amount of money, earned by learning Wayne Industries secrets. We see that Mira is frightened and runs home though the basement. There, she realizes that an object she wanted was left in the batmobile.
In the epilogue of Batman The Dark Knight issue number 5 we can see Mira going to a ship in Gotham's harbour meeting a lot of criminals she was working for. We learn the criminals forced her to work for them because they kidnapped her father, and they would only let her go if she delievered the Batmobile specifications to them. She lets them know she doesn't have what they wanted but something even better: a jamming device against Batman. The leader gangster accepts and tell Mira her father will be spared. As she leaves the ship, we see her meeeting up with Batman telling him she did what he asked.