I suspect that the movie is not particularly good, but not so bad it should be cancelled.
I don't think we can be sure of that. Does anyone remember Catwoman? I would say that's a movie so bad it should have been cancelled. How it got that far despite it's quality, I don't know. But it happened.
Can you imagine how bad it would be for the DC extended universe if Catwoman was released before Justice League? It could kill the momentum of the franchise that many people already view as second tier. Sure, the studio would manage to salvage a few bucks by releasing the movie. But the damage to the franchise could have been much greater than any money they managed to save. Especially depending on how much the content of Batgirl plays into the rest of the Batman and DC continuity.
From a certain point of view, this could be changing point for the DC EU. The day where someone near the top finally said "Stop pushing garbage out the door just for the sake of making movies, and try to make this universe work for a change! No more Suicide Squads, no more movies that require multiple directors and releases." It's not likely. But it's possible.