What he suggests happened is that Lynn seems to have slept-walked through the whole trip not really noticing how concerned her father in law was by the number of things that could go wrong. I should think that not even his anxious hovering around the search and rescue team might have shown her that it was something she might want to pay heed to. If the fact that we're supposed to pity Elly for being blindsided by something that only hateful people who want to hurt her and make her feel bad say that they can predict is any indication, only the fact that he had to be treated for exposure finally got her to realizing that he might have been in serious trouble. Given her clear love for the impressive, manly men who kind of dropped the ball because they were unfamiliar with the newer procedures, it's likely that Rod is being blamed because she won't hear anything bad about men who make her go sploosh.
Her solution to the problem of looking like an oblivious dolt was, of course, to rewrite history so as to make herself the voice of reason whom everyone should have listened to. My guess is that were we to look in at present-day Milborough, we'd have to endure her being the only person who saw the gate and the river as dangerous and April being reckless for not listening to advice never really given. This means that Liz's telling her that the radio said that parents should keep an eye on small children would mutate into Elly remembering that Liz had to be told to keep an eye out for April. Since Elly couldn't possibly be everywhere, this means that Liz got taken advantage of because her mother sense had yet to kick in.