I'm glad that ended well for you, Bopeep. I understand your reluctance to speak, at first. It's tricky for a mil/gp to "make waves" and could end up hurting them, in the end, so I get your thinking this over. And I believe that's wise anyway. Since your relationship with this ds and dil seems to be reasonably good, I don't think there was any harm in letting her know you were uncomfortable with her remark. You didn't criticize her, and she knows she's not perfect, surely.
In the future, it might be a good idea, if this happens again, to gently say something like, "I'm not a good choice of person to be saying this to." Idk. You know her better than I.
Agnurse, I get your points, but it seems to me, Bopeep was more hurt for herself than her ds. I think she has the right to speak up for herself. And yes, parents don't always see everything about their ac, but there was no need for dil to tell her., imo. The one she should be talking to is ds/dh.
Unfortunately, Nansmammy, I think there already is an imbalance in the mil/dil relationship, especially if there are gc involved. That's why I get Bopeep's being cautious and giving some thought to her wording.