She couldn't make a decision. She really wanted time with S6. She let, you, the alpha-male, make the decision. And you did. The only problem is she didn't like your decision. Oh well.
She didn't want to be the "bad guy" and so to S6. She wanted, you, the alpha-male to take charge and protect "her time" with S6.
Next time, say "no" to S6. Respect the mutually agreed upon boundaries.
Don't propose activities with kids during her time. Even if you think your activity is more fun. Even if you think activity is doing her a favor. She'll interpret itas undermining to her.
If it's HER night, let her have it.
Why?
1. It shows respect to her. Very alpha-male.
2. It lets you say "no" to kids. Very alpha male.
3. It gives YOU time away. Gives you more time to GAL.
4. It gives her a taste of her boring life without you. Can't you see...you ARE the fun in this family. She's a tag-along, boring, lonely, depressed, two-timing, dead-weight at this point.
You really are doing her a favor by taking the kids, since she's clueless about what to do with herself...BUT she needs somebody to blame for her misery, so she'll blame you for taking the kids during "her" night. Give her no reason to complain.