First determine if the child that is crying all the time is doing it because they are overwhelmed by noise and confusion, if they are doing it for your attention, or if they are doing it because it is now learned behaviour. Either way this suggestion will work it is just the tone of voice you as the caregiver uses will depend on which of the above you think it is. When she starts to cry regardless of what the others are doing send her just outside the area or to a specific spot to get over it - far enough away that it will be calmer and quieter there. It's like giving her a retreat place - even under a table if that is what makes her happy. The idea is she is responsible for making herself happy again and stays there till she is. If she is doing it for attention going to the cry place will get old very quickly. She may realish the "trouble" the other kids get into for making her cry so unless they are doing it directly to her to make her cry then let the noise they are making go as if it is normal and have the crier be the one to retreat.

I have one that runs from noise and hides in a swivel chair I have near the window and he turns it so he can't see us. He is now 3 and has always been like this. From the time he was safe in that chair that is where I put him to fuss, turned him half way around so he had privacy of sorts but wasn't excluded as in could see us still. From just over 2 he started making the chair go all the way around himself. I am convinced he has issues that need investigating but having a hard time convincing others if you know what I mean. I would either send him to the chair or now once he goes to the chair then I will quietly say something to the other kids that the noise level is getting out of control etc. I never do it in front of him because I don't want him to learn that he can control anything by his running away behaviour.

Sometimes this is when it is time as the caregiver to step in and do an activity with the kids to change the focus off the screaming and crying and then let them go back to freeplay and hope they all have transitioned - a quick story, song, all going to look out the window, whatever, the break doesn't have to be long.