Help! Got new hen and others will not let her go into tractor run.

My three month old hen was killed by a raccoon last week, and I just got a replacement hen to put with the other surviving 2 hens. We have a small chicken tractor, with coop above and run below. I tried the trick of putting her in the coop part with them after dark, but when I opened the ramp to let them in the run, they won't let her down with them and keep pecking and chasing her. I am afraid of locking them back up together tonight, since she has nowhere to escape from them in the closed up coop. Any suggestions? I am afraid that they will kill her, and since I just lost my last chicken I cannot bear to lose another! Please help with advise if you can. I have no other place to put her besides the tractor, as we live in town.