We have two resident cats and we’re trying to introduce a third. For context, the two resident cats were introduced over a year ago with a pretty smooth and quick transition. The new cat has been separated in a room for a month or two. We’ve done room swapping, item swapping, treats together, eating together, playing together, etc. (with a gate between the three). There is usually some hissing and growling from all cats. The new cat is very timid. She barely comes out of the room, even when the other cats are in a different room. We’ve been trying to get her to come out more and explore, but usually she runs right back to her room. We removed the gate and did some small introductions, but the new cat seems terrified. We had them together today and she started growling, hissing, and drooling, and she pooped outside the litter box which she has never, ever done before. I feel like the new cat is way too nervous, and I feel like she needs to go to a home where she is the only cat, but the thought of rehoming her crushes my heart. We’ve brought her to the vet and they said she needs a dental cleaning. Apparently one of her teeth will likely have to come out, and it does seem to be pretty tender. She is going in for a dental cleaning at the end of May (literally the earliest we could do it). I know that pain can sometimes cause these behaviors so I don’t know if I should wait it out and see if there is any improvement after the fact, or if I should just give up now. Does anyone have any suggestions or new ideas I could try?