Can the mother of the groom wear pants at a beach wedding in Mexico or must she wear a skirt or dress.

Pants are fine anywhere.You can be quite dressy in pants as well as a dress.

Here is my thought process... unless there is a reason that you are restricted to wearing pants, I feel the weather and the position you have in the wedding it would be more appropriate to wear a dress. Check the temperature of your son and his bride on your decision, but you may be more comfortable (temperature) in a dress. I stand corrected... I just read in an etiquette guide that pants are okay... check with the mother of the bride on what she is planning.

Wear something that makes you feel beautiful. Weather it be pants or a dress, just be sure it appropriately dressy for the occasion.