Exactly how can a player avoid submitting a wrong score after gaining a retrospective penalty?
The penalty was earned at the time of the breach. On that day the player returned an incorrect scorecard. The player breached a Rule. The penalty applies to the particular hole and the scorecard needs to reflect that.
Lexi learnt of the breach and penalty on a following day. That was most unfortunate while she was still competing in the Tournament.
Forget Lexi for the moment.
You friend, play a comp and unwittingly breach a Rule. Maybe playing from a play prohibited area that was not clear to you or your marker. You return your scorecard. It is wrong because 2 penalty strokes were not applied. You are having a chat in the Clubhouse later and for whatever reason the play of that hole is discussed and it is realised that you breached the Rule, unwittingly. Being a person of integrity you advise the Captain. The Competition has not finished.
The Committee does what it must and applies the exception and applies the 2 PS and additional 2 PS for an incorrect scorecard.
This is a retrospectivity here, maybe an hour or so after you returned the scorecard and hours after the breach of Rule.
It is different but the same in principle.