As others have said, maybe there's something going on in her life. Regardless, that doesn't give her the right to treat you so badly. I would never say those things to a friend. If she is having financial difficulty she could talk to you privately and explain it. I 100% believe it's jealousy--I'm not the "Oh she's just jealous" type but that's what it is.People will surprise you. I asked a good friend to be in my wedding and she excitedly agreed. As the day got closer her attitude completely changed. She started to make snarky comments on everything from our choice of transportation to the flavor of our cake. She didn't buy the dress and at 3 weeks out told me she didn't have the money. (For a $99 dress that she'd known about for 8 months.) Eventually I realized it's her issue, not mine, and decided not to care. This should make you re-think your friendship. Not saying you shouldn't be friends with her, but you should think about how close you are. Close friends don't treat each other like that.
I'm side-eyeing all of these new posters commenting on this thread. There are no WP "responsibilities". Just because it's your "most life changing day EVARRR" doesn't mean you get to stress other people out with it. I can't even remember what the OP was about, but all of this attitude about "my day, my day, you need to do what I want" really needs to stop. Your day will be special because you're marrying someone you love, not because everyone showed up the dress you wanted to wear and jumped how high you asked them to jump.You don't need expensive designer "bridal party" dresses. In the end it doesn't matter. Stop drooling over bridal websites, and go to the mall if budget is a concern. Was the BM a little bit rude? Yeah she was. But people don't usually come out that rude out of nowhere. Usually there's more backstory to it which is what a lot of posters were trying to say.
I agree, maybe she did not budget for the dress this soon? But the coffee idea sounds really good. It might even be something like her health etc. Does she have kids? I do think she is a bit out of line calling your wedding sh*t tho.