My first thought was to ask what are you feeding her, and have you changed her feed lately? Several years back I was feeding 21% protein, and it seemed like my flock guardian dogs were always hungry, even though they had access to their food free-choice. A hungry flock guardian is Not good when there are so many little feathered meat bodies all around them. I switched to high protein dog food with meat (lamb, chicken, beef or whatever you prefer) as the first ingredient, and it immediately made a noticeable difference in their behaviors. A working dog always needs a high quality food, and though a flock guardian doesn't exert as much energy as a canine sports athlete, they are working dogs nonetheless. In addition, I agree with the suggestion to have bloodwork done on her. Not only would I request a standard blood panel test, but hormonal changes could also cause her behavioral changes, and so I would discuss this possibility with your vet too. If you have made no feed changes and blood work comes back normal, only then would I consider her chick eating to be a behavioral problem. As already suggested, don't allow her to be unsupervised around chicks until you have a better read on the problem. Since she has until recently been trustworthy around poultry and also because you adore her, even if the problem is behavioral, I would absolutely try to reshape her behavior to what it was before you consider rehoming her. But rule any medical reasons out for her recent behavioral changes before you proceed.