You just said you wouldn't let her manipulate you. Now she's invited to your activity and she wants YOU to have her over once a week for dinner.
It is her job to work things out with son. And, she should do in on her own. She caused this mess, now it is her job to clean it up! Why are you caving to her bullying tactics?
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!