How sad that any religion would make someone think like this.
If it helps, try to think of her as someone who has a mental illness. She has been blinded by a cult and manipulated into believing this is the right thing to do. It's not that she doesn't love you, it's that she is incapable of seeing past your rejection of her belief system and accepting your choice. This is unlikely to change.
You can love her and wish her well while keeping your distance and not putting yourself in a position to be rejected by her again. Do not offer to let her see her grandchildren, they shouldn't be around her anyway, she will be toxic to them in ways you probably don't see right now.
Focus on yourself right now and your own family. I highly recommend meditation for learning to cope with difficult emotions.