Just a thought - I don't know much about your family or family situations so I could be very wrong . . .

Your mum might want to help you out with the money for the bridesmaid stuff to try and keep the peace a bit and keep relationships between everyone happy. She might not mind forking out the extra $$$ because keeping the peace may be more important to her.

It doesn't mean that your SIL expecting you to hand over that much money is reasonable and I agree with the others - what you and your family do for holidays is absolutely none of her business.

I guess what I am getting at is maybe you should have a chat to your mum about how she is feeling too. I agree that she shouldn't have to, but maybe she really wants to . . . I am speaking from experience of parents that are like this . . . they would rather fork out enormous amounts of cash to keep the peace than have us all upset with each other. I very much think on the principle of the matter and I am not happy if something doesn't seem right and fair, but I also think that my parents don't want to be in the middle of anything and respect them and their need for us all to get along.

I don't know if that helps much, but thought I would throw it out there. Good luck with everything and I hope that it all comes to a harmonious solution