Cass acting OOC like this was a red flag to me, and giving that reason of fighting for Bruce isntead of what he stands for came off to me that she gave that monologue because she's plans to come back as Batgirl, but until then, she needs to concentrate on something else she thinks is more important than patrolling Gotham.
If that's the case, then it's touching that she left the matle of Batgirl in Stephanie's hands. It's an indication that Cass trusts and respects Steph enough to give her that sort of responsibility.