I haven't been around for a while, but I am leaning towards what transform said. The idea in recovery, with detachment, is not to keep a disaster from happening, but not to go out of our way to cause one to happen either.
If she doesn't want her kid around someone who insists on growing pot on their property, I guess leaving the husband and house would be an option. Again, I haven't been around, nor do I know the whole story. But making a decision like that, in the hopes that it will affect the way he will choose to live the rest of his life (being clean while parenting) is setting yourself up for disappointment.
I also agree with the dog comment, I remember back in Illinois an undercover police officer came to the house to question me about some events that happened at a barn I used to work at. One of our dogs was at the front door barking, defending his home and us from this stranger walking in our yard, and before the guy was even halfway up the walk, his gun holster was unclipped, and his hand was on his weapon. He started yelling at my roomate, who came to the front door to find a plain clothes man with a gun in our front yard, saying he was going to shoot our dog. An out of uniform officer , trespassing on our property, was threatening to shoot our dog, before he even made it to the front door.
Be careful what you wish for.