You really need to keep her separate from the others for a couple of weeks, not only to let her settle down but as a quarantine measure in case she is bringing in any infections or infestations that the others aren't resistant to. Maybe you can fix up some sort of wire barrier across the run, with a waterproof box for her to sleep in, it doesn't have to have a perch. Then they can see each other but she won't be threatened by the big girls.
Introducing just one chicken is always difficult. The established ones are never friendly to newbies, but if there are at least two pullets, they pair up during the quarantine period and are not so exposed once they get to meet the older birds. Have you got room to go back and get another one to keep her company? I found that a third bird, introduced later than the others, was never properly accepted and so was always quite lonely, whereas when I've introduced a pair they get on much better.
Is she younger than the others? There will always be ructions when new birds arrive, but it's not fair to put a pullet in with larger, older birds until she is at least 20-22 weeks old as she won't have the confidence to stand up for herself until she is ready to lay. When you do introduce them, there is lots of advice on here about how best to actually do this - don't just put her in with them during the day, this may well lead to bloodshed and will be distressing for her in any case.
Probably best to separate them for now, think it through, and ask more questions about how to go about the next step towards a happier integration for your new little girl.