ldrnomo, the mother has been happy for you to associate with her son despite you not going to meetings for the last 12 months. Have they had a CO's visit recently or attended an assembly?? It could be that she's paying attention to her son at the moment because of something she's read or heard but this may be a passing phase.
Ultimately, the mother has responsibility for her son and the right to set rules. I think the only option you have is to respect the wishes of the mother for now. Make it clear to the son that he can contact you at any time. Maybe after a couple of weeks, check how things are going and she may have softened in her attitude.
penny