First I adopted my three mantras:
1) What I focus on expands (So every time I thought of the things that made me unhappy I would force my mind to more pleasant things)
2) Not my circus, not my monkeys (To remind myself that I could not change my DS's situation so I might as well use option 1 above)
3) No news is good news (To reassure myself that everything in my DS's life was OK and also what I would reply to people who asked how he was)
When my mind wandered to what I now call "the abyss" (You know, that spiraling thought process where I ended up more and more depressed) I would pull out my mantras and say them to myself as many times as I needed to until my mind could focus on something I enjoyed. I planned camping trips, figured out menus, made grocery lists, walked in the woods, whatever would occupy my mind in a cheerful way. My DH and I planned all sorts of camping trips (they don't cost tons of cash) and we went out and had a blast. Then when we called to talk to my DS I was no longer asking him questions about his life, I was telling him how much fun we were having! Suddenly I was not a call to be avoided but one to enjoy, for both of us.
I didn't try to talk to my DIL. As a matter of fact there was a point right after the separation when my DIL hated the sight of me so much that she would meet my DS at the end of the street to avoid me. She has since found a wonderful therapist who has helped her to see things in a different light. The changes in her are amazing and I am sure her life is better for it. I am actually proud of her, which is astounding if you know where I was before. You can read all of my posts on this forum if you want to know the rest. It gets rather repetitive so I can certainly understand avoiding it. Trust me, it was far worse to live it!