It sounds like she's in a very self-centered bridezilla mode right now.
Be patient and kind. Fulfill your duties as a bridesmaid. And then expect her to just disappear for a bit while she's adjusting to her new life as a new wife. If she's a good person, she'll realize she was very selfish and come back.
I'm sorry you're stuck in this. Hopefully, you'll know not to behave this way when you are getting married.
