Vance and Sylvia did it during Season 1 which she confronted them over, but they're all friends now.
Jon is always talking shit about everybody, apologizing, then talking more shit. A favorite line he likes to say about Letty is that she fucked all of production during Season 1 and tried to fuck him too but he rejected her. He also once made fun of her having been physically assaulted by an ex, which resulted in them not talking to each other for a few months.
Jimmy went on a rant the second to last night of 2.5 where he talked shit about Vance and I think about Letty too over something stupid, which TTS told them about.
And Claire crashed out a couple months ago on the FTL site saying Letty is an Only Fans girl, for seemingly no real reason.
So yeah, I think Letty is really sensitive to people being two-faced at this point, I mean she was livid when she confronted Chicken over it.