Her behavior is completely inappropriate and personally the responsibility is on the father who is allowing such potentially uncomfortable contact with his son.
Her contact is most likely a VIOLATION of the court order... dad cannot try to get around the direct meaning of the order using another person. A no contact is a no contact.
I would send a certified letter to the dad and copy gf and acknowledge that her actions are most likely with the best of intentions but put the child in an uncomfortable and awkward position when the relationship is already troubled.
Let your husband know that if HE (not her the obvious codie rescuer being sucked into pitying the victimized dad ...lol) wishes to AT LAST do the right thing and obey the current court orders you would love to see a healthy and happy relationship develop with his son.
The important thing is letting your child know that you are not impeding a healthy relationship in the future but want to teach him that he himself can choose his own boundaries with his father and certainly interfering girlfriend.
Copy the court and if you have a lawyer have him review before sending.
Counseling is always great for kids caught in these sad, sad situations.
My heart is with you mom... been there done that and my kids turned out very healthy and KNOW how to set boundaries with their still troubled father... they are like the parents with him always giving him life advice and even at one point saving his money for him since he was unable to be a responsible person. Dad is some better and I like to think his kids as adults became his role models...
you can't make this stuff up.