The odd thing about Elly's need to make a big, ugly public scene when faced with something that doesn't seem to be her business is that she believed that she had to. What seems to be happening is that Elly sincerely believed that if she knew about Fred cheating on June and didn't say anything, she was helping Fred be a cheating cheater who cheats. In these days of AIDS, it is a public service to make sure that someone is able to protect him or herself from the risk of infection but back then, the advice most people gave was to back off and not blunder one's ways into the affairs (so to speak) of others. That sort of thinking meant less than nothing to Lynn owing to her being a somewhat simplistic and juvenile thinker raised by uptight idiots.
The reason that I mentioned this is because this whole silly arc seems to be based on Lynn congratulating herself on "saving" a friend by telling her that her whole life is a lie. My guess is that her breezy comment about Lynn Lake being populated by adulterers must proceed from her belief that since none of them bothered telling this woman about something that wasn't actually their business, they were all lined up behind him helping him cheat. This also explains why it is that John is depicted as a slobbering oaf blind to the misery that June has been subjected to without her knowledge; my guess is that when Rod caught wind of Lynn's plan to out her friend's husband, he tried to convince her that it was not her place to do so. Lynn clearly took his need to keep silent about it as a sign that he approved of it.
The interesting thing is that this belief pattern is still with her; it explains why she fired her staff and it explains why Elizabeth hates the people of Mtigwaki like poison. In both cases, a shallow idiot who doesn't want to admit that people are too paralyzed with fear because they don't know what the right thing to do it aren't on the side of adultery and making her miserable merely because their legitimate need to not want to get caught up in someone else's problem leads to their not showing up at her door and saying "Guess what! You've been made a fool of!" Given how oblivious she is to the consequences of her actions and how isolated she keeps herself and especially how people cut her a lot of slack for being a jerk because they know that she's not right in the head, she thinks that it's fun and easy because she didn't get much blowback.