Dark Knight and Batman Universe question?

in the movie Lt. Gordon's wifes name was barbara gordon, but if anybody read the comics or watched the TV show they know batgirls real name is Barbara Gordon. so why did they do this on purpose? Batgirl is supposed to be Jim Gordons daughter. I think she made a cameo in the movie but we barely see her, but is she supposed to be that much younger than him? she was like 8 and bruce wayne was 25..??