Help! I have a problem with my new cat!!

Always keep them apart like in separate rooms or something.

Sounds like my cat when we first got my dog. XD And my cat is a psycho.
I remember we kept them separated for a little bit, like having my dog outside and my cat by the window so he could get used to seeing the dog, then we brought my dog in and separated them with a baby gate thing, and we fed both of them treats, distracting both of them and making it more positive... Maybe keep the cat and dog distracted and away from each other until they feel comfortable? The cat might be nervous, y'know new surroundings and stuff.
I hope this helps. It was a few years ago when we got my dog, so I'm not completely sure..... D:'
At least my cat gets along fine with my dog now, whatever we did worked, because I was sure my cat would terrorize the dog the rest of his life. Now they even sleep together.
You could always google it. Good luck!

If you've only had her a while, then it may take some time for her to get used to him, if she doesn't improve I'd take her back, before she ends up physical hurting herself or/and your dog. It will be a shame if you do have to get rid of her, but it might be for the best. :)

Your cat is acting normal. Cats are very territorial animals. Now she considers your house as HER territory, not be shared. As she's the last one to enter the house (your dog was there first), she does her best to defend her turf and chase out the dog she considers as an intruder.

You should have made the introductions first, that is, keep them in separate rooms, so that they may feel/smell each other's presence. Then gradually introduced to each other in changing rooms in which they were kept.

Now, have separate territories for them both. It's like for people, you know. The dog was there first, he has his own territory. The cat is territorial and needs her territory. Assign rooms and places to each and not to be trodden upon by the other. It may take time and both of them may not end up bosom friends. But they could at least live in a comfortable indifference.

You may also ask your vet some advice.

my cat be she passed away would try to play with my dog my cat would hiss and attack him i think its because of mistreatment we adopted my cat we didnt no about our cats past just treat the cat the best u can hopefully i may help