You agree that she will be having doubts over everything. And yet, around her she has these posts that are undermining her authority at best and attacking her at worst. I admit, I come at this from a different perspective because I have been in her situation. My garrison has often faced that choice, where the lives of the many are weighed against the lives of the few. Sometimes you have to surrender a battle in order to win the war. So, I personally agree with her. It does not make the situation any less horrific, any less terrible and I suspect she knows that.
So, really, does she feel stabbed in the back by your sister? Does she feel betrayed by the people around her? And if she does, could there be some validity to her feelings? If I were her, when I've been her, I would feel very alone right now. Maybe that's how she's meant to be.
I just think that you going out to do what she has already arranged to do could start you down a path you will end up regretting one day. If you trust her, let her do her job.