My uBPD+dOCD s2bx is from a wealthy Mexican family
Her expenses will be based on her living expenses here in the United States
I will be paying her alimony
What happens if she moves back to Mexico and lives rent-free?
Can I get a reduction?
I'm guessing you do not having anything spelled out about this in your divorce order? Mine says if I move in with someone or get married, alimony is off the table. Mine also says if I get an increase in salary, alimony goes down. If you were concerned that she moved back to Mexico where the cost of living is lower, I think you would need to get that into the order. And show that her new cost of living is xyz.
You can always try to show a change of circumstance, but like FD says, that is a tip off that she needs to change her game. And my guess is she would figure out a way to justify that she needs alimony.
I don't think a court would look too favorably on a motion for this, is my opinion. If she wants to go live somewhere cheaper to make her alimony stretch, that's up to her. A court might think she's being financially astute. Unless you call this out in the original order and she agrees to it.
However, if her decision affects custody, that's another matter. In my state, it's all but impossible to move when there are minor children involved, even if you have sole custody.