For myself, I'm content to let it slide this weekend and this holiday season. Give MIL time to cool down.
I this is a good idea. You've got enough to contend with given the very-fresh reconciliation/departure of OW without throwing gasoline on FOO flames at this exact moment.
Good point, Kett.
Gardener
"My soul, be satisfied with flowers, With fruit, with weeds even; but gather them In the one garden you may call your own." Cyrano deBergerac