I have 2 german shepherds and from early puppyhood, they had to learn that they cant chase 'my' stuff. I have cats and the gsds are high drive working dogs. I was very firm with my corrections when they wanted to chase cats. If voice or scruff shake wasnt good enough, they would get a prong collar and drag leash (I think I only had to do that to my 1st puppy 15 yrs ago--my training got better since then!).
Introducing to the chickens--both dogs (singly) got to say Hi to the chicks with me being protective (in my hands and using body to deflect dog). If they showed too much interest, they got growled at. The dogs were always allowed to safely supervise our interaction with the chickens. I did make the mistake of thinking I could get the dogs to herd the chickens a little. That caused a huge conflict of instincts. They were being very good not even noticing the chickens (not looking at the chickens is deliberate doggy language), with me asking them to follow and move after the birds, I ended up with my young one jumping on one when it darted. I yelled no, he backed off immediately and I decided not to be stupid any more. My dogs will range out with the chickens (eating chicken poop.....) but will not acknowledge the birds. They do, however, alert me to chicken noises and some predators. I do use the dogs as predator deterrent and so far so good. If a dog tells me that he hears something, I immediately respond and let him out. If the chickens are out, the dogs will completely ignore them as they look for the cause of the noises (sometimes one of my stupid cats--so now the dogs are learning that they can, indeed chase the cats lol!!)
With out seeing your dog's intent (some do want to kill, some are merely turned on by the movement of a prey animal), I cant really say an e-collar isnt necessary. But I would start with less aversive methods. My attitude is that the dog must always know what is yours and part of the pack. I would start holding chickens with the dog near you (hold safely so dog cannot get the chicken) and correct the dog verbally if she shows too much interest. Technically she cant even sniff if you dont want her to. Next step would be a long line and loose chickens. Let the dog wander and if she is too close to a chicken, leash pop (as hard as necessary to get her attention) and a verbal correction. See how she reacts. Herding dogs have high prey drive (plus herding instinct) that is trained and controlled. Most herding dogs still need to be trained and shown limits before they stop making 'mistakes' (harassing the livestock)
Never allow unsupervised time and dont let the dog make a mistake that you cant back off of (killing a chicken). If things go well on leash, keep a long drag leash on and make sure you monitor the interactions. It is always the human's fault if something bad happens. After 6 months of interactions, I really trust my dogs at this point. But they are still dogs and if something happened, I will be disappointed, but have to take responsibility. Good luck!! An Aussie/Lab mix sounds like it could be a great working dog!!