What should you do when your mother disapproves?

I got engaged a few days ago to my live-in boyfriend my mother does not approve of. When I told her over the phone she didn't congratulate me or say she loved me although I did. She thanked me for calling. I will be very sad if she doesn't come to the wedding which I suspect she won't. He sent a letter to her a while ago apologizing for a time that he and I had broken it off. However, she called him a non-entity and is the kind who holds grudges. I know she eventually wanted me to leave him. How do I deal with her absence at the wedding and maturely handle her ignoring me?