Kat, Shara is just swearing a lot and getting angry at people do deal with things. Just like you told her, a little while ago.

↓ Transcript
Shara: So ... I'm sorry I didn't manage to warn you, either.
Katharina: It's not your fault.
Shara: No ... but it would've been even better than cleaning up after the fact ...
Katharina: Well, thank Lhûn you did THAT. You and ... the sword. Without you we'd all be dead.
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<Beat panel where Katharina looks sad and Shara looks at her>
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Shara: ... you realize the same goes for YOU, right?
Katharina: ... w-what do you mean?
Shara: Obviously you think this is all YOUR fault. Am I wrong?
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Katharina: N-no ... of course it's not. But then again ... this whole expedition was MY RESPONSIBILITY. I am the one who should have -
Shara: BULLSHIT!
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Shara: LISTEN, Kat.
Katharina: S-shara ...
Shara: Are YOU the one who planned this stupid trip in the first place? I DON'T THINK SO! Are YOU the one who thought it'd be a good idea to partner with a fuckin' MOB BOSS?! PISS OFF! Maybe once we're back it's time to go to your Master Peck and ask him WHAT THE FUCK HE WAS THINKING? 'Cause I don't know about YOU - but I can't wait to hear how HE expected this to end!