Sorry JR, but I think I would have let this one go. A brunch always takes more than an hour, so I would've taken your W's promise of "an hour or so" with a shovel of salt. And then when she didn't return w/i an hour, I would've just gone on w/ whatever you had in mind to do w/ the kids -- and just send her a text saying so. "Kids & I are going for a bike ride, then probably grab lunch. Should be back in two hours or so. Enjoy brunch."
I think not being her doormat doesn't mean critiquing her when she misbehaves, but going about your own life as if you don't care.
Speaking as one who is still in in-house-separation, and one who gets pulled into W's stormy waters ....
Me: 50, MLC/WW 45 Young kids Nov 2015: BD1 Apr 2016: BD2 Jan 2017: W filed Feb 2017: D final