I expressed this fact and she asked me, “Where in the bible does it say that a couple must be married in a church setting”.
This is such a non-typical response for a practicing Catholic, that along with some of the unanswered questions above, it seems evident that more is going on here than just getting married in a garden. I wonder if a priest is presiding, and if the wedding couple has gone through the pre-wedding inventory and classes that the Church requires. The Catholic Church places a lot of importance on pre-wedding education and activities, and rightly so, because it is one of the few faiths for which marriage is considered a full sacrament.
I admire the fact that you are troubled by this proposition. Fortunately, it does not involve one of your immediate family members, and it does not seem that you are being asked to be an active participant. I think as a practicing Catholic, you are obligated to point out where and why you think your friend is going wrong here. But then, you are friends with the mother of the bride, and ultimately the bride and her husband-to-be are probably going to make the final choice. Therfore, you will have to decide how you want to participate, or not, in this ceremony.
After the dust has settled, or maybe even before, I would say that you have a lot to discuss with your friend in light of her response above. It seems to me that you could provide some needed enlightment, correction, encouragement, etc. Maybe this is the real opportunity for you to gleen out of this situation.
Sincerely,
rocket.rob