Good job HTTE. I think for where you are, you did just right with the birthday and just right to tell her that when the kids are older, they will in fact know about what she did and that she destroyed their world, not you.
For W's birthday, I made a cake and cooked dinner, but, we haven't had things out yet. That will be tomorrow. I'm both looking forward to this and dreading this conversation/confrontation tomorrow.