how do i handle different beliefs
I'm so sorry about your situation.
I actually go to church twice a week and I can say what your ex SIL is saying is wrong, I have relatives who are not religious and we respect what each other believes. I only talk about the bible if my relatives ask me about it. Preaching to you in a forceful way is silly and even I know that a person who suffers from anxiety needs to see a good GP and counsellor.
If your ex SIL doesn't accept your beliefs, it's best like others have said not to have her around. In time you will find some respectful friends.
I hope you can work things out for you and your children.