I, for one, don't think you should be so worried. First of all, it's not a good idea for her to travel when she's so far along in her pregnancy - especially if she has never been to Mexico before. The risk of her having a sensitive stomach and/or getting sick for ANY reason is not worth the danger to her baby. Hopefully her doctor will convince her of that.
Secondly, most reasonable guests know full well that the bride is the center of the show. I've been to many many weddings in the last few years and there's often one person (i.e., inappropriately slutty guest, drama queen aunt, etc.) that screams for attention. Most guests rightly choose to ignore these people and appreciate the wedding for what it is - a celebration of the couple's union.
Your best path forward is to make sure that you look fabulous, that you feel great about your new life w/ your hubby, and that you appreciate your friends and family who will, in fact, be there just for YOU! And be sure to lean on your other BM's who will give you the support, time and attention you need to have a happy wedding