This particular Ask the Expert actually comes by way of the New York Times and Peggy Post’s Wedding Q&A column, because unlike most sticky etiquette situations I read about, this is one I can’t say I’ve heard before!
A step-mother who threw a bridal shower for her step-daughter in June and contributed financially to her wedding in September just found out that none of the guests have received a thank-you note for either event, is horrified (obv), and is wondering if she should just start sending them on on behalf of her delinquent step-daughter!
Ms. Post’s answer is great. (In short: Brides: Um, do not do this. And concerned family members: No, you cannot send thank-you notes on someone else’s behalf; yes, you may kick the bride in the butt.
Whew. Take a look.