Mike,
The tournament officials were informed of the possible breach when the last group was on the 14th hole and Wie was on the 15th hole.
Also from LPGA.com:
Q. When did the spectator bring this up?
ROBERT O. SMITH: I was sitting on the 15th hole. The final group was on, what, Jim, 14.
JIM HALEY: Yes, somebody else asked me the same thing. I think it was about 40 minutes before the tournament was over.
Perhaps you would have preferred that they haul her off the course immediately to resolve it. Since there was no way this could affect her future play in the tournament there was no point in telling her before she finished the round. If it was a possible violation during the 4th round, they might have said something to her earlier as knowing she might have a penalty might cause her to play differently.
If you read some of this or the Bees and Wie thread you will see that Rule 34 sets a specific time limit which is when the tournament is officially over. According to Kendra Graham on Golf Central last night the LPGA declares a tournament over when the money list is released to the media. Obviously they didn't do that until this was resolved.
To those who say that the official should have ignored a report like this or that the rule should be changed so that he could have ignored it don't realize what a bad situation that could put an official in. Lets say a person somes up and says, I saw Vijay Singh take a bad drop. The person seems credible so I investigate it and determine that he did and penalize him. Later another person comes up and says, I saw Tiger Woods take a bad drop, but the person seems flaky so I ignore it. Aren't I opening myself up for charges of favoritism? By requiring me to investigate every incident and by investigating them all as thoroughly as possible I'm assured that I never get in that situation.
Bamberger has said he wanted to ask Michelle about it first. If he did ask her about it on Saturday, she should have gone to an official then or Sunday morning and gotten it cleared up.