Chickens have a pecking order, and this is normal behavior, to establish a new pecking order when there is a change in members of the flock. An new member is normally automatically at the low point of the pecking order, so it will get pecked the most. Introducing a new chicken often requires things like housing them side by side for a few weeks with a fence between them, to allow them time to get used to each other, then supervision when they are actually put together. At this time, things like offering treats, having a separate feeder and waterer, and having them in a large area with hiding places will help.
If the new one is bloody, she will need to be removed from the flock until she is healed. Chickens will continue to peck a bloody wound, often to the point of death. Then you will probably have to house them near each other but out of reach for a few weeks.
When already together, if severe pecking occurs, sometimes you can identify one who is the "lead bully" and isolate that bird for a week or so. Then when you introduce it agan, it will be at the low point of the pecking order.