I would say that your T is trying to get you to establish and think about what YOUR feelings are regarding your mother's comments, how does it impact on you. In other words you can clearly see your Mother's point of view and opinion, hence how easy it is for you to defend her, but where is your view or opionion, how do you feel when your mother has said something particulary hurtful. You are separate from your mother but you only voice your mother's opinion not your own, do you know what that opinion is? T wants to hear your voice not your mothers. That's why you are there in therapy, its for you and your voice! Its hard to acknowledge that our parents can be complete idiots at times, they are not perfect, it doesn't mean we don't love them any less or that they don't love us any less!