What bugs me about that, "You're not good enough," line is this; they always called her back.
Batman refused to let her work. Until he needed her to get hold of Tim. Then he called her in again. When that pissed Tim off Batman took up training her.
Then came the murderer arc, where he went crazy and disappeared for a while. (He didn't actually fire her that time.) And then she was called back to help when people needed to prove his innocence.
Then he, in Gotham Knights, gave her a test and she failed. He told her she wasn't allowed on the street. Then came either Joker's Last Laugh or Batman: Family, both make reference to her being called up for duty by Batman again.
Then she gets the usual discouragement. Right up until Tim quits and then she's okay again. Then she's not.
If you go strictly in-continuity, without the meta or the guessing at a writer's intentions, or characters-as-plot-devices, what you have is the Batclan telling her that she isn't good enough, right up until they need her to help them out. If they can break their own rules for self-serving reasons, she should be able to break their rules too.