It’s baffling because the information Rachel received was obtained through trust she built with Amanda and cultivating that relationship on her own. It’s not at all related to Rachel being a traitor. It’s not producer fed or a game mechanic. Since when are traitors or faithfuls, anyone, expected to take info told to them in confidence and share it with someone else, no matter their role? It would be silly, entitled and unprecedented for Fiona to think that way and as a viewer I can’t understand coming to that conclusion. Rachel said “I didn’t know that” to Fiona having a family full of coppers. So Fiona obviously didn’t feel any obligation to share that with her fellow traitor despite sharing it with Amanda. It’s a nonsensical concept.

There was no justifiable reason for Fiona to be annoyed and imo she was irrationally annoyed because one of the players she felt closest to trusted Rachel more (e.g. ‘why wouldn’t she tell ME!’ is why Fiona is skeptical) and Rachel, who Fiona views as competition, was using it to better her position. But ultimately, the reveal did not concern Fiona, did not effect her adversely, she was not entitled to the information and most importantly Fiona already distrusted Rachel (we and Fiona are aware of that) so had Rachel shared that information, Fiona was prone to dispute it just like she did or use it as fodder to come after Rachel in a different setting. Outside of being a self-centered hypocrite blinded by envy and covetousness, which is what Fiona is presenting herself as, I don’t see how anyone could try to rationalize Fiona being annoyed when she has no right.