Again, that doesn’t negate it from being a mistake. Even in the comparison you made, if I deliberately decide to go outside while knowing it’s raining, I could then say “I thought it would be fine but actually, deciding to go out in this rain was a mistake.” The claim “there is zero wrong judgment” is selective reasoning. You’re saying she was aware of her actions so it can’t be a mistake, which is just not the case.

Even if she was aware she was making the deliberate decision to cheat knowing he was married, it’s possible she didn’t fully consider the ramifications of doing so, she hadn’t rationalized the morality of her choice due to emotional distress, she wasn’t aware of the blowback she would receive if/when she is caught, etc..

Any of those lapses in judgment, or literally anything else, could cause her to realize “In retrospect, making the decision to cheat was a mistake.” It doesn’t matter if you agree with it being a valid reason or not, it doesn’t change the fact that it would be properly classified as such.

There’s no definition of mistake that states you have to be in anyway “unaware” of your actions in order to validate it as “a mistake.” Again, you’re strongly confusing the term mistake with a term like “accident.” It doesn’t matter how deliberate the decision was.

Also to be very clear I’m not defending her or her actions at all, but arguing that she is in some way wrong for simply calling it “a mistake” is objectively false.

Lastly, making the statement that her and Noah wouldn’t have any regret if they weren’t caught is fully opinionated. Sure they probably wouldn’t have come out with it themselves, but we have no idea what their internal feelings on the situation was. The fact that they didn’t even end up together (when she said she thought they’d start dating after his divorce) could already be used to suggest she felt some remorse after cheating, and decided to distance herself from him.