I am thinking about changing out of the bridesmaid dress after the ceremony. What do you think?

The dress was pick by the bride and another bridesmaid who are both size 6. The other bridesmaid in a different states is a size 8 and I am a size 12. The other BM's don't have any kids but I have three, my youngest being 10 months. I have breast feed them all and my breasts didn't go back to their original size, one is a size bigger then the other. I sent the bride an e-mail asking if I could pick a different dress because she chose a short strapless. I have a hard time holding the dress up, if you know what I mean and even adding spaghetti straps don't help. If I bend over the wrong way you can see possibly see my imperfections. Anyways I have decided to just wear the dress. This is just the beginning of her ridiculous nonsense. I will end up spending 2 grand on this wedding with no help from her. My two daughters will be her flowergirls. I had to pay extra for the plane ticket because she changed her wedding date three months before the wedding and I bought it two weeks out and the price increased 100 bucks per ticket. I tried booking the hotel where the ceremony/reception is two months before the wedding and she had not confirmed the contract with the hotel or something and I couldn't get the wedding deal. I tried booking the hotel two weeks out and I was told by the hotel that the wedding reservations close a month before the wedding. I will have to pay 800 bucks for three days at the hotel instead of the 310 with the wedding party deal. The only way I could possibly get to bypass this is if she asks the wedding coordinator at the hotel to give me the deal. Because of her indecisiveness it has cost me a lot more money then I planned on spending. She doesn't seem to care that I need her be a little more lenient with her dress selection as well as informing her wedding party of need to know information. She is not offering to pay for anything nor does she let me know her plans with the flowergirls, any desires of hairstyle or anything. I will never agree to be a brides maid again and does she really think that I'm going to wear a Malibu colored sleeveless, short dress again? I don't think I'll ever be 12 years old or going to prom. $150 bucks down the drain! I'm wondering if our friendship is even worth this? I feel as though she just doesn't care about how her bridesmaids are going to look next to her, I really look a fright in the dress and I'm sure she is not going to like her wedding photos. She's busy with all her wedding plans and I will just support her the best I can with my dress open on top. I will not bend over the rest of the night. I wish I'd never agree to be in her bridal party.