New Dog Is Aggressive to Resident Dogs?

It can be a very slow process that requires a lot of consistent and positive reinforcement for good behavior and no response to bad behavior (after they are separated of course).

There are so many good videos on YouTube how to do this. Find a few that are specific to your breeds if you can and check them out.

If that does not work, then you may need a professional trainer. We had to go that route...but our case was our resident dog would not let the new kid in.

We had one session with a trainer and got peace in the house. It was a miracle. She taught us techniques to de-escalate and manage the old girl's behavior.

Sadly there are times when it never works. I have dog sat for dogs where there is an upstairs dog and a downstairs dog and never the two shall meet. It is not easy, but sometimes it has to be down.

Prayers for easy solutions!

First off how old is the new dog that you brought home? I see here that she is a female but you did not say what the older dogs are. If she is still a puppy she could be wanting to play with the older dogs but they are not interested in this. If she is older she is use to being the only dog in the room and does not want to share. I would start off slowly and get them in the room together and hold on to her. Make sure you let her know that these dogs belong there and so does she.

You need to do this in stages and allow the dogs to smell each otehr and get use to each other. You may need to keep her apart for a week or two and only allow her out when you are in the room so you can watch her, sit with her, and talk with her. Bring in the other dogs slowly and make sure you are petting both dogs at the same time and let her know that it is fine.