@deecol you aren't hijacking the thread. other brides have surely had similar situations and will appreciate to hear how you have dealt with it. they may think they are the only one with a mother that has tried bargaining with their daughter, or made a stink about a decision they've made that is so important to them. get it all out - it helps all of us!
this is a day (and a week) to celebrate you and your FI and you should do what truly makes you happy. it is your time to be selfish for once in your life and do what makes you (and your FI) the happiest. i agree 100% that one should not reward bad behaviour. it seems as though you have had to almost take on the motherly role in the relationship between you and your mother. although i can't relate, i commend you for continually being the bigger person. not to contradict myself when i said you should do what makes you happiest, but knowing your mother the way you do, think about how she will react if she does not receive some sort of special "shout out" (in whatever way, shape or form it is)...will she take this out on you on your wedding day or wedding week? would it be easier to throw something tiny in their to appease her and possibly prevent a scene?!
i am not proud to say this, and it is something i work on day-in and day-out, but i can be spiteful. i have a problem letting go and not taking things personal. if this was my mother, i would also have a hard time honouring her when she was putting me through so much unnecessary grief, BUT, looking at the big picture, it may be easiest to appease her and save yourself the worry the day and week of.