This reminds me of a pet peeve of mine, western medicine! You go to a doctor for one thing and they give you some sort of drug to treat that one thing...but it causes some side effect. Which, when you tell your doctor, they too often treat this new thing as totally unrelated to the first thing or the drug given for that. And on and on and on...When she was younger we had a trainer come in for her chasing the cat and the trainer suggested a shock collar. Then my puppy pulls really bad on a leash and the trainer suggested a prong collar. So we have been using that.
Sorry, but as I said it's a personal sore spot...
On to doggy issues. You need another trainer! Any trainer that uses an ecollar to get a dog to leave a cat alone, is not just clueless, they're going directly against ecollar manufacturer's instructions! So as Joanne said, lose the ecollar and teach the dog that the cat is a friend.
Easier said than done, you might be thinking LOL! But it really isn't if you take it slow. First though, it requires your dog have some prior training. Once your dog has a solid "down stay" and "leave it" commands, introduction to a cat is easy.
Keep the dog on a leash as a backup, put her in a down stay and let the cat in. Remind the dog as needed using "leave it" and stay, and just let the cat be a cat. Eventually, the cat's curiosity will cause him to investigate the dog. This may take days or even weeks, but cat's at some point can't resist once they feel sure the dog won't get them.
But even if the cat does not come over to see the dog, simply coexisting in the same room without chasing will get them both used to the concept.
Eventually (but don't rush it!) you can allow the dog more freedom of movement, still leashed for safety, as long as she doesn't fixate on the cat. If she does, call her back and make her lay down again. Rinse and repeat. They'll be friends, or roommates at least, in no time.