Dont feel bad dab.. Mine chase things all the time, and Femka ( the rescue) has treed a black bear twice, and bite them.. The first time the bear went up a tree, and she bit him in the behind, and the second a larger bear went up the tree, and the limb broke and the bear fell. Then the bear smacked at her, she twisted in mid air and promptly bit the bear on the face- riping the mouth.
I have to watch for small things alllllllllllllll the time. Sighthounds are awful for anything small and moving. I mean think about this- if they will chase a white plastic bag in lure coursing chasing is to the bone in instinct here. The joke is- we have some old deer ( bucks) that have figured out if they walk the dogs wont chase them if they are out. A chicken would run and cause commotion and it would be hard for a dog not to chase them. Once chased, the next follows.. The only little thing that survives here except for my vigilance in watching and letting the wildlife know we are out there, is the possum. Once they faint my dog will walk away.
Its a sad fact but true living on the top of a mountain. We have wildlife allll the time. I always open the door to the screen porch, turn the tv on loud, go sit out there and talk to myself.. ( rofl) to make sure the wildlife knows I am around and out. And none of mine are cat safe=. If it runs, its fair game.
May I suggest training her. Meaning put a check cord on her when outside. Thats like a thin lead but like 20 foot long. When she goes to chase the chickens pull her back and scold with a firm NO!!!