There is a " statute of limitations" actually. It is called completion of the competition. The competition is played over 72 holes & then the results are confirmed & posted. Once the results of a competition are finalized they cannot be changed except in exceptional circumstances. The officials, once they were made aware of the rules breach had no choice but to penalize her. As for this issue of home viewers ringing in and reporting these incidents, I am in 2 minds. One, it seems totally unfair that only some players in the field are under this type of scrutiny purely because the TV is following that group. but 2, Do we really want someone to win a competition like this when it is obvious that she did not play within the rules ,be it due to carelessness or intent?
I dont think external viewers should have any say (via email, phone, or social media), especially a day later! For majors like this stick an official with every group (I think they do?) and its their job to "police". If they or their playing partners don't see anything then all good and round is complete.
Optionally have a couple online officials watching from the camera viewpoint.
You are right viewers are only seeing the top players so theoretically the others are at an advantage. Maybe not to win but can move up places in score if they were to break a rule, on purpose or not.