Moms of married grown kids

I am the mother of grown kids. My son is married x11 years, has a 6 year old. He and his wife are having problems because her caught her cheating. They are trying to work through it, but he was a preteen when my own marriage fell apart due to my ex's repeated cheating. Since this is his wife's second time cheating, he feels that they are done and is just trying to be civil until their situations get settled (separate living places, custory, finances and all that stuff...).

I still speak to DIL, but have told her that I am hurt by this and am sad that my son is so sad also. Well, her mother just call me. She is telling me that I need to speak to my son and basically get him to forgive her, to tell him that people make mistakes and that it is my responsibility as his mother to tell him to stop being hurt and let it go!.  I told her that it is really none of our business and that all we can do is support our kids, remain civil to each other, hope for the best, prepare for the worse and keep our grandchild as happy as possible.  She has called several times since, insisting the same.

I don't think I should but in because this is a very personal, intimate problem that they need to work out.

What can I tell this lady??  I dont' want to stop communications with them, but I'm at by wits end and she is MAD at me.