Thats a tough one, and there is a line I think on what we talk to our kids about and what we leave out. Shame D7 knows OM is mommys lover ... shame mommy has made that mistake and exposed D7 to this ... again not much we can do. My S8 also knew, but he did not care for it and the R between him and W paid a price, one she will have to fix .. thats all her and not my circus.
Its a tough question because you do not want to paint W in a bad light, and its a critical point because none of us wants our children to have marital issues later in life due to what we the parents exposed them to at this stage, regardless of who the WAS and LBS are .... but it does seem a bit unfair being the LBS and knowing we have to fight fair while the WAS can paint the M as bad as possible and the 'reason' they just had to leave.
To answer your question, this is just me, I would apologize for snapping and just calmly explain this is not what you wanted for her nor the family but regardless of things outside your control you will be there for her, the rock .. no matter what.
Others may have a much better approach on this, I would just shy away from making anyone out to be the 'bad guy'
