I would definitely pick her up on it. The issue here is that she's not only bullying you and your son, but your grandchildren so if you take a strict line as I do where child safeguarding is concerned, you'll tell her not to fill your grandchildren's minds with the idea that somehow they're descended from worthless people. Your dil is responsible for instilling ideas about family rivalry - very immoral.
Would you think it was odd if a younger person wanted to befriend you?


.
