Starting Over Talk

Can someone who saw this movie explain to me what the deal was with the segment on the Mexican Housekeeper? I am so confused about whether or not she took the kids to Mexico and if her whole tragic saga even happened.

In the beginning she has a phone conversation with Brad Pitt's character where you see the conversation from her perspective and you hear his voice saying they aren't ready to come home yet and he pleads with her to stay until they get home. She tells him that her son is getting married and she cannot find anyone to take over in the care of the children so he says okay. Then he calls back and tells her she HAS to stay with the kids...so begins her sad story.

Then in the end of the movie the same phone call, (the first one)is replayed only from the Brad Pitt character's perspective. The same phone call transpires, (including a portion where he talks to his small son) only after she tells him about the wedding he says he will have the wife's sister come to relieve her and that is where it ends...no second phone call. Huh?

Are we to presume the whole thing never happened?

I'm going to watch it again just to make sure I "got it" but if anyone else is confused or gets it please let me know!

Thanks!