That sucks! I'm so sorry to hear about the drama. Although I don't think there's any wedding that's ever been had without some sort of drama. I agree with Mufin1785. You can either go at her from the angle of "I know that you have alot on your plate, I'm sorry I put the added stress of being a MOH, would it be easier for you to just be a bridesmaid?" or just ask your sister to be a co-maid of honor. A couple of my friends had 2 maid of honors and no one thought it was weird (in fact, in each situation it was a best friend and a sister to the bride). Plain and simple, whether you guys have grown apart or not, what she has said and done is SHITTY. But, if you want to keep the friendship and keep things civil, like I said, just go to her with concern for her busy schedule and offer to either have her be a regular bridesmaid or tell her your sister wants to be a co-MOH. Good luck with everything!