I agree with the breeder. There are people that say you need to keep them separate for a couple of weeks to make sure the new ones don't have anything wrong with them though.
We have introduced new ones twice. The first time we did keep them in a neighboring run where they could see each other for a couple of weeks, but when we did introduce them it was mayhem, and we had to separate them again. It took months to integrate them.
The 2nd time we just waited until the old ones had gone to roost, then opened the roof and placed the 3 new ones in with them. They didn't even notice until the following morning when they seemed amazed that these new girls came out of their house! There was still some pecking and the usual establishing of the pecking order, but no blood drawn, and it too less than 2 weeks fr them to all be at ease with each other.
As you will only have 1 to introduce new ones to, she won't be able to bully them all, but she will be the top hen and may boss the new ones around a bit.
Just make sure they have more than 1 food and water source so they can't be kept away from it, and that they have somewhere to run to (my new ones hid under the hen house when they were chased).
I am really sorry about your calder ranger, but good luck with the new ones.