I think it's perfectly reasonably (and healthy) for you to draw the boundaries you need to draw with your friend and her wedding. After five years of therapy, I believe very strongly in doing only those things I feel comfortable doing and saying a polite "no" to things that I'm not. It took some training to accept that the only person who really needs to be okay with those decisions is me. I'm not advocating being a selfish or self-centered person. I do plenty for the people I love and care about, but what I do for them is not motivated by guilt, unrealististic expectations, or the like. In turn, my friends know me well enough to implicitly trust my sincerity.

As that applies to your friend, politely explain that you can't do her X because it conflicts with your Y. If she gives you grief for it, say I'm sorry you feel that way; I'd be happy to help with the wedding plans at a more mutually convenient time. Then walk away (mentally, at least). How she reacts to you taking care of you is her problem, not yours.

As for your friend. Her behavior is just not acceptable. Planning a wedding NO MATTER HOW BIG is not a license to act like a spoiled brat. Yes, brides-to-be get obsessed and stressed, but only so much of that is tolerable. Calling a friend a cow is just not right. And if this is just bringing out some tendencies in your friend that you already knew were there, please ask yourself whether she's a friend worth having.

I was in a wedding early this year. There were a few eye-rolling moments for me with the bride, but in all fairness to her, she always kept her cool and was very mindful that all of her bridesmaids had other time and financial commitments. It turned out to be a pleasant experience for all, and our friendship is as strong as ever.

So, while I agree that you will likely have to grin and bear some wedding related craziness, you don't have to be abused, sign your life over, or suffer silently as she acts like a brat. If she can't handle a polite "no" or heart-to-heart about wedding etiquette, then I'd rethink being in the wedding at all.

Just my two cents.