With D2 involved, it will be near impossible to be dark. All I can really do is not respond to anything that isn't about something important regarding D2.
If she brings up the sale of the house and/or mediation, my simple response will be-
'I have said before that XXX is the mediator we will use and it will cost approx $XXXX. When you have your half saved, make an appointment and I'll let you know if it works for me'
A friend suggested I delete her from Berry Messenger. And I know a few (looking at you, Steady) will say I'm still concerned with her feelings but I'm not sure that it won't make 'the wrong statement' and/or will require me to tell her 'email only'.
For my own purposes, her intermittent 'status updates' and 'profile pic' changes make me think and I'm quite sure most of them are 'pointed' at me. So there is a valid reason to delete her. Her last "Wishes life was 'normal'" was laughable. The responses pretty much write themselves. A friend suggested I change mine to "Slowly returning to normal". But that is "engaging her" and showing her the 'buttons' still work.
But I'm not sure if deleting her sends the 'door closed' message. Keep in mind, I have been reminded by a few folks that "I don't want a divorce, right?"