I need a sounding board to help me with my MOH.  This weekend is our bridal dress fitting on Sat. afternoon.  After the fitting the bridal party are going to go out afterwards to eat and have a few drinks so that all the ladies can bond a bit and get to know each other.  This is the first time they will be meeting my MOH who lives 2 hours away.  We have had this date and time planned for 2 months now.  Then all of a sudden she decides that right after the dress fitting, she wants to rush off to the local BMX race track to get her son signed up for the Saturday night race. (This is not a planned championship race, just for fun). 
I let her know that this last minute change in her plans upset me and that she was coming into town for the dress fitting, NOT for her son to go race.  She knew that Saturday was supposed to be dedicated to the bridal party.
And this isn't the first difficulty with her either, she wants everything done around her budget and her schedule and her convenience.
Any advice?