How might you have handled this visit from an ex-sister-in-law?

Recently the ex brought his sister with him when we were exchanging our kids. When he arrived I got out of the car to speak to him about an issue having to do with our children. This is completely permissible according to the terms of our parenting plan. As I was finished speaking (he was not receptive to what I had to say) and was walking back to my own car his sister got out of the car and stepped up on me in what was a clear attempt to start a fight. When I told her I wouldn’t get in a fight with her, she and the ex responded with a string of shouted abusive epithets – in front of the kids. Later that evening I received an email from my ex accusing me of verbally assaulting him and his sister.

Fast forward two weeks. My ex-sister-in-law shows up at my house with an iced coffee and an apology. She and I were never close during the time I was married to her brother, but never really hated each other either. I had no idea this woman even knew where I lived. She claimed her brother did not know she was there but that she cares about the kids and didn’t want this between us. My family had just sat down to dinner when she knocked and all of the kids were stricken with terror when they saw who was at the door.

So what would you have done?