I am so very sorry that she was acting out this morning. None of you needed this BS at that time of the morning, if ever. There's no excuse for bad behavior...but she's not a happy camper and things aren't going the way she thought they would. If she said 7:30, then she should have been there at 7:30 and not at the time you were getting the kids off to school. That a "shame of her" deal.
She may apologize and then again, she may sweep it under the rug. Time will tell. Continue as you have been as you are the only adult in your children's lives at the moment.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.