It's not throwing her under the bus to say that she chose to get the divorce. You don't (and shouldn't) tell kids the sordid details, but it's also important to let them know some of the realities.

And as Mowgli points out, if your W can't handle saying she chose to end you marriage, maybe she's not ready yet.

Me-38 W-38; T-15 M-12;
S10 and S6
BD - July 2016; EA confirmed; confronted Aug 2015
EA dissolved 12/2016

Never make someone a priority when all you are to them is an option - Maya Angelou