I was thinking the same thing -- maybe a goldfish? But you're going to have to do a welfare check on that fish!
Mealworms or scratch, with a tiny scoop and instructions "only one scoop per day" would be ok. But how could you be sure that neighbor limited it one scoop, or knew what day it was?
Yes, you've got yourself a lonely neighbor, and she's definitely exhibiting some signs of dementia. If she's doing this in public, just imagine the private life? Is she remembering to turn the stove off? Has she backed her car into the fence a lot? Is she eating more than just Nutella and toast?
As much as she is *not* your problem, you share a space, she's impacting your chickens, and you want her behavior to change, so she kinda became your problem. A knock on her back door, with some mugs of tea, and the bag of mealworms, "Would you like drink tea with me, while I feed the chickens some treats?" might be a sanity saver.
I wish you the best of luck.