Okay, I am going to be the bad guy here, but she makes a point about forgiveness. You may not be ready to go there yet, but your children will benefit from it. He may not deserve your respect, or your love, but everyone deserves forgiveness. I am not saying you should respond to your MIL, but at some point, you may want to consider where she is coming from. You will only enhance your children's agony over the situation if you cannot forgive. They will feel a need to "take sides" and that only perpetuates the unfortunate circumstances. I believe she means well. Only you can know for sure.
L