Parents Whose children have been sexually abused Community Group
This group is for parents whose children have been sexually abused. We welcome both Mothers and Fathers. Here, we can offer support to one another. We can vent, cry and lift each other up. No condemning or criticizing allowed. We are here for support. We LOVE (((HUGS))) !
As for the teacher, you will give away nothing private simply by telling her that, while she couldn't possibly have guessed, there's an estrangement in the family, and it makes your daughter uncomfortable to hear about her grandmother. You can ask that she not share any information about your daughter with your MIL as MIL has lost her grandmotherly privileges including hearing about your daughter.
However, I suspect you would do even better if you were to share the gist of your situation with the teacher -- again, tell her there's no way she could have known this. But she is a mandated reporter, and she can keep an eye out for your niece/nephew, as well as for other students with whom your MIL may come into contact. I'm assuming you haven't prosecuted, or your MIL would be banned from situations that put her into close contact with children, such as those school functions.
I'm so sorry that this has happened to your daughter, and that she is suffering again. Of course, this means that YOU are suffering again. Be strong, do what you can to protect your child and others. Then, let God hold the weight you can't carry, and keep moving forward for the sake of your daughter.
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