To remind you: Shara has already told Katharina about Gideon, and how he talks to her –  at least in broad strokes.

↓ Transcript
Shara: Look, we TALKED about this! He's NOT EVIL. He just wants wants to get OUT OF HERE! And he didn't start the killing - that was Lady V!
Katharina: But she did it to get her hands on it! Didn't she? And didn't you say the SERPENT EMPRESS could also be after it? We're ENDANGERING EVERYONE if we're carrying this around with us!
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Shara: So what, you're just gonna LEAVE HIM? Tell me: what do you think will happen if one of them FINDS him. Something GOOD?
Katharina: <sighs> ... no, I guess not.
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Shara: Exactly. So we HAVE to take him with us, see?
Katharina: ... maybe. But Shara ...
Shara: What?
Katharina: That's ... not the reason YOU want to save it, is it?
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<beat panel>
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Shara: ... "Him", Kat. He's alive. And I just ... want to help him.
Katharina: And you are SURE "he's" not -
Shara: Yes. Yes I am.
Katharina: ... right.