I have yet to read anything from anyone that shipped their OOT bag goodies down ahead of time, and from things I've read, the resorts tend to dissuade it. everything could end up getting lost before you even get there! you're almost ahead of the game by buying extra suitcases and paying the extra charges for baggage because shipping to Mexico is definitely NOT cheap!! as long as you pack the small sanitizers, Tylenol, etc that generally goes into the OOT bags and don't take it all on board, you're good. they've relaxed a lot of the restrictions that were out there for liquids and stuff. but be careful because I heard something about duties going into Mexico. You need to have your receipts showing how much you paid and I seem to remember reading something about they had just raised the limit, and I think you're allowed $400. maybe somebody that knows a bit more about it can chime in and help out with that part of things.
good luck to both of you and happy planning!!