No matter how able you are to contextualise what she said and why she might have said it, it is painful thing to be on the receiving end of such statements. I am sure you don't need mothering advice from a childless stranger on the internet, but it is ok for you to hold your boundary of self-worth and tell her that you don't want her to speak to you like that. Obviously, a time and a place for that discussion, but it feels important that you don't lose yourself amongst your ability to care for and empathise with D.