"That was a long time ago," Sam gently reminded her. "This is the now. I think you've proved yourself more than trustworthy at this point. And I think, yeah, it's okay for her to have her issues with you, but to bring them up now? With all the stuff you guys have going on? It's inexcusable. There's a lot at risk and you guys can't afford to be fighting with each other like this. If she's gonna carry on and give you all hell over the past, then she needs to back out and not come back. Because at this point, I think that the future is what she needs to be worrying about. Not the past."
They were at war. Every day. And if Buffy wasn't willing to stick her neck out for other people without complaining about it, then she obviously wasn't mean to fight in it in the first place.