Is this social worker breaking any rules?

My sis and bro in law are foster parents for our local human service dep.. They are wanting to adopt. I have went to the dep. with them ONCE, to allow the bio. parents and grandparents a visit with the children.( they have removed the children from thier homes but they have not legally lost ALL rights) The social worker allowed for the childs family to walk us to the car and and buckle them up. After the social worker went back inside the building the mother proceeded to throw her Burger King cup across the parking lot and scream about one thing or another. My concerns are they live in same city and I thought this could be VERY dangerous they know what one of thier vehicles look like and so on. Just being a parent myself I know people can go to extremes when the posssibility of losing a child is real. I know if something was to happen there would be great consequences for them, but the fact still remains SOMETHING COULD HAPPEN. So is some rule being violated in this case or am I over reacting?