It would be hard to like a mother in law who has not tried to be nice, and maligned your wife to other people. I used to have a mean and jealous mother in law, so I sympathize.
I don't know your wife, but it sounds like she must be a decent person if she is polite to your mother when she sees her. However, I would not let spite be any motivation for any type of behaviour, one way or another. If your wife is going to be the best wife and mother, then to "rub it in your mother's face" should not be her reason or motivation. It is wrong to carry hate in one's heart. I used to be very sweet to my mother in law (I'm divorced from her son now but not because of her!). When she said rude or self-centered things, I just pitied her and let it be water off a duck's back. We only saw her on holidays, and lived across town- so I didn't have to deal with her very often.
My advice to your wife would be to continue to be polite, and patient. Adversity can build character. And try not to hold animosity in your heart. Prove her wrong about you.
My advice to you is to level with your mother. Be kind, but tell her that she has been very hurtful to someone you love dearly, your wife, your chosen life mate, and she is hurting you when she is unkind to your wife. While you want to respect your mother always, you want her to respect your decisions as an adult. You may have done this already, as you say she has not said anything else to your faces.
I can tell you, as a mother of a 14 year old son, I look forward to being part of all the big events of his life. I hope I will like and approve of the woman he someday chooses to marry, but there is always a chance I won't. It seems like yesterday he was little and in my arms, now he spends all his time with his friends and doesn't know I exist. Sometimes it is hard to let go.
I know this is a difficult situation, so I wish you luck. God bless your home and your relationships.