Attacking Cat...Help!

Hi Everyone

So my boyfriend has moved into my house and he has brought along his 2 dogs Gibson and Pearl.

Pearl is an 8 1/2 month old boxer who has never seen a cat before moving into my house. My cat is a very dog friendly and usually puts the dogs in their place at the first meeting and then everything is good...however Pearl is another story.

My cat is 12 years old and declawed so he is basically defenceless especially against a 50lb zoned in boxer puppy!

How can we get her to stop fixating on the cat and trying to attack him? And if/when she becomes fixated how can we get her out of it she just becomes out of control when she gets in this "attack" mode. She hasnt actually bit the cat she is just pouncing at him and snaps at him and will chase him if he runs. She barks and her tail is wagging?!?!

We have tried "leave it", water bottle squirts, cookie, and now I am just picking her up and moving her to another room. I spanked her the first time it happened because she was after his tail.

And another side note, not sure if it is relevant or not, but she seems to only be "attacking" in the evening after she has eaten her dinner. She has even let him walk right by her in the day time without a second glance.

I am so confused and dont know what to do.

Thanks
Jenna

PS. We declawed the cat on the recommendation of our old vet and we will never do that again because he has had to have corrective surgery because of nerve damage. So please do not hate on us because of that we recognize the mistake and still regret the decision to have it done.