First of all, I think I agree with your mom. Your mom has a grandchild, an important relationship. Your mom needs to maintain a relationship with the mother of her grandchild. That isn't comfortable... but it is a fact. You and your new wife are going to need to deal with that.
You can not force your mom to have a relationship with your new wife. That is between your mom and your new wife.
My advice to you is to focus on the things that you can control.
- You can have a good relationship with your new wife.
- You can have a good relationship with your mom.
- You can be civil with the mother of your son and try to be decent and cooperative when it comes to your shared child.
- You can be a good father and maintain a relationship with your son.
- You can not make your mom like your new wife.
There is nothing wrong with you expressing to each person what you wish... you can tell your mom "I wish you would connect with my new wife". But that is all you can do. After that, accept that you have done what you can. Drop it; anything that is going to happen will happen between them and have nothing to do with you.
But you have to accept the things that you can't control. You can't make people like each other even if you want them to.