Re: Hopefully someone can give some advice
Coming from a Spanish family, I can see your problem. The big issue is that her family was to close and she cannot accept to be separted from them, she is scare that the separation will make her lose all the contact with her family, bacuase of the distance, something new is scary. I went to this withdrawal when I moved from my country to the US. And the fact that she has continued seeing them every few weeks is not helping, she really needs a longer separation from the family to accept the change.
I believe that you should talk to you father in law, and tell him that the best way to get her to see that the move is for the best and accept the changes easier, will be for them to not come to NY for a few months, you can get together in NY or Florida, for B-days and holidays, but not as frequent as you say. If she sees that the separation from the family is longer it might help. Since you FIL has realize the issue, he can help with MIL and talk to your wife. Do not buy her tickets, she can be away from her parents for six months and not die. It will be hard, but she can talk to them anytime she wants, just get your FIL help to make the mom also understand that she needs this move and telling her to move back and that she misses her too much and that she can live without her, is not helping. He can handle you MIL and you will see the changes will come, take it from somebody who has been there.
You can be forceful without being mean. With the help of your FIL and your loving forceful way, she can overcome this.