Even if it hurts to say no to her coming home at this time,
you can't put your kids through the trauma of another cycle of witnessing
her self-destruction.
What is best for them?
A stable situation, with you sane and your spouse hopefully embracing
the support she must have to get and stay sober.
Right now you cannot be that support alone and she is in no shape
to fix her addiction herself.
So sorry about this very tough situation.
But nothing will change if you let her do what she's always done,
so be strong and loving and let her seek recovery if she will choose it.
You, as the stable parent, must be the rock for your kids.