Have you tried repeating, over and over, until it's ridiculous, her situation back to her? ie that you will do as she did, and WAIT until you're 45 and find such a great guy with such a great ready-made family, lucky her, big smile, hug and kiss, end of sentence, end of DISCUSSION. And look sad about your "real mom", wherever she is, and the fact that this hag made you remember her. And shut her down, that's the only thing to do to old people, I am one, so I know. Especially mean ones. You're only 28, nowadays that is pretty young. It's your brother's wedding, that is going to be FUN!