By support, I would think she means providing a neutral and non-judgmental space in which it is safe to talk about thoughts and feelings, as well as express thoughts and feelings. Her role as good mother is probably more about eliciting the thoughts and feelings directly, rather than through an intellectual filter. I suppose psychologically it might be about expressing whatever to the good mother that the child could not express in reality to the bad mother.

As far as Object Relations, this is one of the most readable sources I've found to give a mostly clear explanation of the theory, and how it can inform practice: Object-Relations & Self-Psychology: A User-Friendly Primer - Barry Joseph Weber, David L. Downer, David I Downing - Google ƒuƒbƒNƒX