Counseling is not an option while there is still an active affair going on. Most professionals, even on the "non-exposure" side of the aisle, would agree with that. I also have D18 overhearing her mother telling her brother on the phone that "I'm only going to go to counseling so people will think that I'm trying," and she's given me the same impression and I also confronted her with the "overhear" and she didn't deny the comment.
No, I don't have any guarantees that this approach WILL work. I am fairly certain, however, that if I DON'T do it, I have zero chance.