Dog from shelter attacks cat - advice?

Does anyone have any advice?
My sister adopted a 7-year-old spayed female dog from a shelter on Thursday. She brought her own dog there first to see how they got along, and the new dog was OK - she growled a bit, but didn’t show her fangs, and seemed to get used to the other one after a while. The new dog had been tested around cats at the shelter and had ‘passed’ - she showed no aggression toward, and in fact no interest in, the test cats.
But now the new dog has tried to kill my sister’s cat. (Or did it sound worse than it was?) When she introduced them, the dog showed no interest, and everything was fine. But later that night evidently the dog attacked the cat - my sister didn’t see it, just heard the yowling. So she separated them, and tried to introduce them slowly.
No problems until today. This time the new dog attacked the cat while my sister was in the room, and my sister said she looked as if she was trying to kill it. As well, she has attacked my sister’s dog twice - my sister’s dog is smaller.
The new dog seems very docile and sweet, but every once in a while she attacks. The cat did nothing to provoke her.
What should we do? We’d hate to take her back to the shelter, but the cat is scared and hiding, and my sister’s dog looks nervous.

If anyone has any ideas, I’d appreciate them.
Thanks in advance.

Looks like either the new dog or the pre-existing pets have to go. If it were me, I’d get the new animal out of the house asap. The cat might run away now.

not a match. The new dog should not take precedence over the existing animals. It needs a home by itself. or it will kill the cat.

and probably hurt the other dog as well.

Do yo really think there is no way to slowly get the new dog to accept the others? Has anyone ever tried to get an aggressive dog to accept a cat, and succeeded?
She’s such a sweet dog when she is alone. We never expected any trouble at all.

What I would do is keep them apart so they can not physically be together for a week or two. They will smell each other and could end up being pals. Its certainly possible.

Has to be managed properly.

Introduction must be slow. One week at least in separate rooms, introducing first smells -favorite towles, smells impregnated items- then supervised, short visits for another week.

Animals that are strangers to each other should never be left in the same room alone, especially a shelter dog whose issues have to be worked on. Not because he was given teh OK at the shelter that means he can join teh pack seamlessly.

Separate immediately in different rooms, reintroduce gradfually, from smnells to sight to supervised games.

The cat will run away. No cat is going to remain in a place where it is in constant fear of attack from a bigger dog. The other dog might accept its new role as subordinate to the new, aggressive dog, but I doubt the two dogs will be happy together. I think the owner needs to seek the help of a professional animal trainer.

Thats also true, you dont want to save the life of one dog and put the lives of the other two in danger.

Well, the cat and new dog have been separated, but how long this will work is anyone’s guess.
If we did take her back to the shelter, what on earth can we say? My sister doesn’t want her own pets to be unhappy or in danger, but if we take the dog back she’ll probably be euthanized, especially if we tell them she attacked the cat.

Its a tuff situ. YOu need to work it out as best as possible. Its the animals lives that are at stake. Just a bother to us at times, but its their life.

I took in a cat because it would likely have been put to death. My neighbor had to find a place for him on short notice as she had to move out.

Most adult cats wouldve likely been killed at the shelters. And he turns out to be an absolutely wonderful animal.

Gentle and very affectionate and a really good cat.

So do work with them. They may well work out a workable solution pretty quickly.

My persian cat and i went to live in a house with 3 other cats and a dog. Their cats and my cat all got along really well after a week of separation. The dog was never friendly to any of the cats but kept his distance and the cats kept their distance. Everything worked out.

At this hotsprings place on YMS there was a dog (big one) and the owner came across two abandoned kittens. In short order the dog killed one of the kittens. But after the owner kept the other kitten safe from him, in a few weeks, they became fast friends and the dog would allow the kitten to climb all over him and he not only tolerated the kitten but took care of it. So good things can and do happen.

Best of luck to you.

from a cat’s point of view, I think you should put in some shelves or bookcases that the cat can jump up to and escape from the dog. Cats can jump much higher than dogs and this would allow “separation” in the same room. Good luck and please don’t give up.