What we know and the two of them do not know is that there is a very real possibility that Irene saw Connie as being the other woman. It seems to never have occurred to Elly that her panicky, angry comment about how if Ted and Connie had gotten married, he'd have fooled around on her with Irene could easily be rearranged in such a fashion as to make Irene the one being made a fool of. It's as if she's a character in a novel by Turtledove who simply can't think certain things. What Alternate History Guy seems to ignore is the fact that Elly doesn't want to see that someone she doesn't like might be the victim of someone she does like. It's akin to how she and Liz never really bothered themselves with the pointless and meaningless question "Why, since Liz doesn't intend to cause trouble and is as surprised as she is that they always seem to run into each other, is this Therese person always insanely jealous?" because they don't like the answer "Because Gordon is trying to repay his debt to the Pattersons by destroying their enemies."
In the prior case, Elly and Connie don't want to see that the latter looks a lot like 'the other woman' because considering the viewpoint of others might make Clingy, Needy, Man-hungry, Crazy Connie look bad. In the latter case, sympathy for the civic devil might make the Pattersons feel like entitled creeps.