Your words "family event"...... nope that's not what it is and you need to stop viewing it like that. Contact legal aid or whatever free legal advice service is called....
All she is doing is playing the power card, she may very well be afraid of you being alone with the kids BUT the parenting plan you sent to her clearly explained your family would be there. So she of full of sh!t.....
I am NOT saying to be a jerk but you should NOT gauge if something is working by how nice/warm she is. You aren't going to get her back by being nice.
Me: 35 husband:39 Sons 16 and 11 from my first marriage Twins 5 (boy/girl) Daughter 3 Affair bomb 2/27/14 He moved in with ow 3/13/14 OW kicked him out 6/15/14 4/2016 he seeks help for sexual addiction