ok - you dont get it - you dont listen - So why ask?
I do get it; I think you don’t. You have missed the point made repeatedly: that (A) no verbal agreement was made during the hand, and (B) a custom followed universally is not collusion.
As long as a custom is followed by everyone, without prejudice toward any player, it can’t be considered collusion. It’s just considered standard by this group.
And indeed, it is what occurs in countless tournaments in both casinos and homes. People check it down when it is in their own interest, to increase the chances of a knockout. All that is illegal in casinos is saying it out loud.
Anyway: home games are free to have their own rules and customs–whatever the players agree to, for the health or fun of the game.
A group could play Hold ’Em where the ace is only high (no wheel possibility). I wouldn’t like it, and it is obviously not standard, but as long as everyone is in on it, there would be no unfairness.
Take an example from investing: If a CEO withholds info about his company from everyone except his close friends and family, that raises the prospect of insider trading. If he makes it public, everyone knows and can act accordingly.
And BTW, this player did not even know what the term “check it down” meant. She was just an inexperienced player who had never really considered concepts as simple as bubbling, stack sizes, STP ratios, or even that TP weak kicker is not that strong a hand in a three-way all in.
The idea that she would not benefit from learning the game, and should be sheltered from even slight embarrassment from dscussion of rules or customs, would not be a favor to her.