Ranger "Refugees" - [5th campaign, 1st mission]

In short, I'm replaying... it's frustrating, my hero was surrounded... And can I wait for her in Biar's castle? It's still more convenient to deal with her behind the walls!

I think you can. The main thing is to kill her after you are given this task, and this happens the day after she takes over the outpost. It's not worth waiting in the castle (although I don't know if she will try to capture it), she is easily killed anyway.