I know you're joking pokey, but not everyone can be exactly like us, I think it's a good idea to be tolerant of as much as you can. If she decides to not be a bridesmaid, she can say goodbye to the friendship. Not in a "we lost touch, we'll be friends on facebook" kind of way either. She'll talk shit about her for years every time she talks about her wedding.
If a woman asks you to be in her wedding, and you don't say no right away...you really can't back out of the wedding at that point and keep the friendship. I'm sure there are some circumstances, but not many...