D. - I looked at your older posts and it looks to me like you have been battling with this woman and family for a while now. It probably won't get much better unless both you AND mom-in-law can find some sort of common respect for eachother. Some people are so hard-headed that she may not be willing to accept you.
Keep that in mind as you decide to get married. Yes you are marrying this man, but unless he plans to disown his whole family, then you are basically marrying his family too. MILaw will be in your life the rest of your marriage, and quite possibly the rest of your life if you and fiancee have kids together.
Who knows why she doesn't like you - perhaps it's the fact you've been married already, or because you have kids, or because she just doesn't think you're good enough for her son. I think all moms are highly opinionated about who their son picks to be with. So it might not be the religious thing. Maybe she's never happy, or like you said - is hung up on your fiancee's ex. Maybe she just needs to get to know YOU better. She needs to see you taking care of your fiancee, see you hugging your kids, see you cooking your fiancees favorite meals. (SEE you doing this not just hearing about it.) Who knows, she may just come around.