Why is my sisters' biological mom so unfair to us?

she should, and i hate to say that you're more mature than a women twice your age. and it doesnt say much for your half sister that she didn't have the to stand up for what she wanted on the biggest day of her life. it's a shame, but you cant dwell on it. and there's nothing you can do about it. Evil Mom will have to deal with it on her own.