My brother is getting married at 10 AM in October. It is to be formal, although I know it is not usually done so early in the morning. This is what the bride wanted. The bridesmaids dresses are floor length. When my Mom bought her dress we were told that the MOB was wearing a floor length as well. We also thought it was going to be at 11AM. The colors coordinate so she is fine in that department. Now the MOB is saying she is going to wear a shorter dress. I'm not sure of the length or formality. Is it okay for my mom to wear her dress? She loves it and feels really good in it.
While it is not appropriate to 'up-stage' the bride or her mother, it seems appropriate for your mother to wear her dress if it had been fine before. It is unfortunate the MOB changed her mind.