I mean, could they of set it up another way? Yeah, but compared to all the other Batman movies this shyt was done a helluva lot better than the other movies though. To me, it didn't take anything away from me. I guess cause I literally never read the comics first for any Marvel/DC experience, them adding extra shyt like this wasn't something that made me cringe, I mean I get what your saying that it was unnecessary but it could of been worse.
But the source material wasn't much to add onto and I think they wanted to keep it as close as they could and giving Barbara and Batsy context made sense to me.
Then again, I'm the muthafukka that loved the Angry Birds movie so
I'd say there's a way to give Barbara something to do other than making her a little girl with a crush, which is ultimately what happened. The context is she's batgirl, he's batman. That's enough reason for him to be pissed and go after joker. That'd be like saying they needed to make Jason and Batman have a sexual relationship to give context as to why he was so pissed Joker killed him