First off, welcome !
[quote]
I’d also like to point out, for the record, we’re all GROWNUPS, in age. I’m the youngest, at 29,
she’s 34, brothers are 34 and 36. I’d be a little more understanding if she were 12. Wait. No, I
wouldn’t. 12 is old enough to act better than this. [/quote
This says it all for my armchair quarter back prognosis.
Weddings, pregnancy/birth and Funereals bring out the worst of human behavior. (If you think she is bad now, see what happens when a close family member dies and it is time to divide up the deceased’s loot. That’s a laugh riot.) This flakosaurus has been with Joe for seven years and is not married yet.
She is:
a)Jealous that you are doing the ultimate walk down the aisle and can get “your” man to commit to you ( and she can’t.) She suffers from no self esteem and is very manipulative, or haven’t you noticed that yet?
b)Her behavior on how she is treating you is exceptionally immature. No woman who is a friend of yours would do this intentionally. She is a not a friend. It is time to down grade her as “passing acquaintence” " You’ve met -insert name here - Joe’s girlfriend.Oh, look, there is Aunt Sally, I *must * thank her for the fondue pot!" In the old days, this would be known as the “cut direct” except you would never talk to them in public. You would be cutting them directly from your social circle.
c) You could “Kill her with Kindness”. But do you really want to be a friend so someone like that? I’m not saying to be mean, I’m saying, be civil when she is in the same room with you. But when she is out of the room she is out of your mind
d) If Joe is such a spineless doormat and cannot stand up to Physcopathic Would Be Bridesmaid From Hell, then let him back out. He will be showing his true colors and jelly fish self. He is not the friend your fiance thought he was.
e) In an unbiased - if possible - manner, tell your bridesmaids ( your sisters, right?) the situations you’ve explained. Ask their opnions. Maybe they can run block for you on the Name issues and divert Whatsherface’s attention from palavering on about her surgery or whatever bug is up her ass that day. Make it a team effort to cover her, giving dipshit all the attention she needs to balm her nuerotic pathetic self, yet sheild you - The Michael Jordan of the team from pesky bugs. Make your bridesmaids *earn * those little trinkets 
f}Above all, do not let her ruin your happiness or come between you and Mr. Smashed Ice Cream.