Right or Wrong is hard to say. Yes, its good that she has a better life now than the one you could have given her. But if it were me, I would have left my husband both for myself and my daughter. Some people don't believe in divorce. But if you do, maybe you should have considered getting rid of him and keeping her.
I suppose if you couldn't do that at the time (seems you have now), then giving her up was a far better choice than aborting her or keeping her. There is no solid right or wrong. There is only levels of good and bad points. As for your mother... she's going to have to come to terms with it. But what people fail to understand is that our decisions in life not only effect our own life, they effect the lives of others as well.
Your decision denied her the ability to know her grandchild. And I'm sure that stings very badly. But you're both going to have to come to terms with your decision and move on. Its already made. There isn't any taking it back. You can't rewind time and make a new decision. Both of you will need to learn to live with what is already done.
You did what you thought was right. That's all anyone can do. Look at all the varied responses you got already. What is right for one person isn't right for the next. Isn't viewed as right. All we can do is what we feel is right and live with that decision no matter the results. Talk to your mother and try to explain that. Let her know that you understand her hurt, that you hurt too, but that you did what you thought best for your baby.
I wish you the best. Take care.
And Samantha, maybe her son came after her daughter and after she left her husband.