Having been through the same thing my advice would be to not get involved, I know that's difficult as it's awful to see your DiL upset , I learned the hard way that blood is actually thicker than water in most cases, I loved my ex DiL we had a great relationship we were Nanny and Granddad to her two children from a previous relationship and the daughter they had together. Our son met somebody else and left his wife, we supported her 100%, he treated her badly and I hated him for it, I refused contact with the new girlfriend and stuck by my DiL, two years later she met a new man we were so happy for her, and then her and her children dumped us like a hot potato, I was devastated and cannot describe the hurt I felt, jump forward to now and I have a good relationship with my son and his new wife and two delightful little GDs, his oldest daughter is a super wonderful girl who is very close to us but her Mother and step brother and sister don't even acknowledge us, I am still so hurt that they could cut us from their lives, I have learned a valuable lesson and that is to stay neutral and never get involved in our sons relationships, they have changed me as a person, I will never allow anybody to get so close that they have the power to hurt me again