I am not a psychologist but if this happens every day when the older kids arrive, I would suspect that there is something she is afraid of at that time. She may not have the words to say to explain what is happening to her. Perhaps you can get someone she trusts to talk to her to see if she can tell that person what has been happening. This worries me some. There seems to be something serious going on, and someone needs to figure out what it is. Do you have a school psychologist who can help you with this?