except one pullet that stalks them and chases them as soon as she sees them.
She is probably low bird in the older groups pecking order, they are often the most aggressive to newcomers, either to keep their place in the order or because they finally have someone lower to pick on.
Putting that bird in a wire crate right amongst the others for a few hours a day may help break the habit as well as gibe the newbies a break.
What does your coop and run look like?
Pics might help garner some solutions.
The more space, the better. Birds will peck to establish dominance, the pecked bird needs space to get away. As long as there's no copious blood drawn and/or new bird is not trapped/pinned down and beaten unmercilessly, let them work it out. Every time you interfere or remove new birds, they'll have to start the pecking order thing all over again.
Multiple feed/water stations. Dominance issues are most often carried out over sustenance, more stations lessens the frequency of that issue.
Places for the new birds to hide 'out of line of sight'(but not a dead end trap) and/or up and away from any bully birds. Roosts, pallets or boards leaned up against walls or up on concrete blocks, old chairs tables, branches, logs, stumps out in the run can
really help. Lots of diversion and places to 'hide' instead of bare wide open run.