First, I said basically the same thing Aunt. I told her to be nice, take the high road and just explain is just wasn't possible to continue to be in the party. Offer the dress to a replacement BM if need be. Wish her luck.
She did that, and the bride told her off saying she was now on her Sh*t list, and they weren't friends anymore. The former BM can't say she's all that torn up about it.
I got another email from the bride under a different account name. She sent it after I had "regretfully" declined attending her wedding as well. (It's on Christmas eve) She told me she would just forward her address to me then so I knew where to send her gift, then told me where she was registered.
I'll take the high road once more, and send her a nice card congratulating her on her wedding, but I'm not sending her a gift. Especially considering not one thing on her registry is under 100 dollars.