Given her problems, seeing a counselor every three weeks is far too infrequent. I believe she needs to see someone who specializes in children's sexuality and abuse. Dr. Toni Cavanagh is such a specialist. I'd encourage you to contact her at her office in Pasadena, California. It would be worth a phone consultation to find out how you should proceed in this matter. It seems the law and these mental health professionals have not helped much. Your daughter is probably caught up in knowing she's been part of something wrong, yet I'd guess she will try to protect your husband based on his telling her not to tell what he's done to her. Please do not accept the present treatment of your daughter as adequate. She is clearly very troubled and this situation demands very skilled specialists to help her.
Keep me posted as to your progress.