Clearly this is not the visitation envisaged by the Court and is in fact unsupervised. Your remedy is to go back to Court and ask for enforcement of the visitation order. That order itself should tell you whether the mother is in contempt. Contempt is usually a two stage process: you get an order commanding the other party to do X; the other party does not comply; you then have to ask the court for a contempt hearing where the non-complying party gets to explain their behavior. Usually in family court contempt orders are issued after egregious behavior and disobedience of an order specifying that contempt is the punishment for non-compliance.
I'm not a KY lawyer and can't advise on specific State law where you live but generally speaking the remedy if someone is not complying with a Judge's orders is to file a motion with the Court to force them to comply with the Order or hold them in contempt. However, if the rehab center owns the apartment and comes round every night it's not clear to me whether has she formally left the facility or whether this is part of her treatment and rehabilitation ? Also do you know for sure that her Mother is not around when she has parenting time with your son ? Before you rush off to Court, I would first talk to the rehab center and the counsellors there about your concerns to see whether appropriate supervision can be put in place for when your son is with his mother.
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