Detaching is the single hardest thing to do for me. It's damn near impossible. I mean, we all want a great relationship with our spouses and the things we are going through are emotional torture. How can your feelings not be tied to what he or she does or doesn't do? It's hard, but it's a lesson we all need to learn and I think Michelle would tell us to detach and move on no matter what.
That being said, as for the text about your S, it's hard to say. Maybe just a text acknowledging that you knwo that's a tough thing for her to deal with but not actually offering her any solutions to the problem? I'm certainly no expert here but that's what I think the book might say. Best of luck to you in a difficult situation.