Weirfan From the standpoint of it could be called because the contest was not over, I kind of see it. The fact that they hit her with a penalty, AFTER the round and THEN penalize her for signing an incorrect score card over something that was so tiny and I must believe unintentional, is crap. I know there are 72 holes to be played, but that's not really the layout, it's 4, 18 hole contests, which cumulatively determine a winner. After the 18, I think that's the end of the contest. Not called? Too bad.
Look at it from any other sport, as soon as the next play, shot, game, etc happens, it's OVER. You call it in the moment, or you don't, it's the only fair way. Everything after that could have been/ likely would have been played differently, if the knowledge of this "violation" had been served. You have officials walking with you, either they call it, hell let them review it in the moment, or it's over.
The USGA is on this, "grow the game" kick, well then let it be played and not convoluted. It's awful right now.