Oh hun....

You have every right to be cut, it was way harsh of her to demote you simply because she wanted another couple to be partners! The groomsman played no bearing on who i picked to be my moh and bridesmaid. Sounds to me like you have a case of Bridezilla on your hands.

Have the dresses been bought already??? I would just be honest and tell her you hate the dress, and cannot/will not wear anything strapless and above the knee. Let her know your reasons, and if she is a true friend, she will understand, and hopefully compromise and find a dress to suit you.

In regards to the days doing this and that, simply tell her you cant attend, or go for an hour or 2, you have other commitments, and she should respect that.

HTH