Letting go is difficult. It still takes my breath away when I think back to when the kids were small and we were all together: the beach, the park on swings, Christmas, Disney World...I'm sure you understand.
When I read about how you handled the situation when she came out of the house, I felt great just living through your actions.
Remember this: She chose to have this happen, you didn't. We all live with the consequences of our actions. If she wants to get angry at you, so be it. You need to slide the "Emotional bar" to the right when it comes to how you respond at this time, because you're no longer trying to save your marriage, you're trying to detach and move forward. Maybe if the M. was still on the line, quickly fixing the toilet and leaving would have been the thing to do, but, again not now. I think you handled it beautifully. All business. You certainly don't want to be a miserable human being about it, and you weren't. Just the facts , m'am. Who car if you have to pay for it. You owe everything to your kids and NOTHING to her. Again, not in the form of retribution, but as you said, firm, discernable boundaries. Nice job.
As far as Cs. go, I always found this board to be far more helpful than the $185/hour I used to give my therapist who would always say: "What do YOU think?" why would I care what I thought if I'm paying you to help me?