I'm not sure how your situation will pan out. But, I can share my experiences. Thirteen years ago, we got a new kitten from the Humane Society thinking our one year old cat needed a playmate. We brought her home and introduced her to our male cat. Right from the start, she was the one who did not like him. There was a lot of hissing and gnashing of claws for several months. But, they did finally settle in together. They even played with each other after about 6 months. They have had a love/hate relationship for the past 13 years.
We brought a dog into the house in May. The cats both hate the dog. The poor dog can't walk anywhere near them without getting hissed at and jumped on. I have a feeling they will never really settle in to the idea of the dog being their friend. They are old, crabby and set in their ways.
I think your cat might settle down. I can't guarantee anything, but you never know. Time will tell.
