Well,horses can colic from hen feed, I had it happen to my horse. Especially if they aren't used to grain.
They are only bad if they eat a lot of it....ask me how I know this! My draft mare broke into my harness shed and ate 25lbs of chicken mash...5 and a half days at a specialized vet clinic, I.V.'s and lots of meds. Thank god no founder either out of all of this....but it was touch and go. So, saying it is poisonous is a lot different than saying it can cause colic if a lot is eaten.
Your hen is a Rhode Island Red, they are good layers, and careful on the corn as it can make them fat or cause a lot of fatty build up around their liver, both will stop a hen from laying and/or cause harm to their health. We give our flock of 19 hens and one roo a wild bird seed mix as it has all the good stuff in it, flax seed, black oil sunflower seeds and a little of the small seed but not much. Putting her water in a black bowl shouldn't be a problem, as I have our two chicken water bowls are the heavy rubbermaid ones so they can't tip them over. And also, that is a hen, no roo there to worry about. She doesn't have the neck feathers nor the tail feathers or "saddle" feathers that are long and slender. No spurs can be seen, though hens can have small spurs as well.
If you want to worm her, put a capfull or two of apple cider vinegar in her water, but it has to be in a plastic bowl, not metal. Give that to her for a week then stop, it also will help with the Ph of her stomach to better utilize food and digestion. Be careful giving her anything that is moldy, molds can cause bacterial infections or bronchitis in chickens from the mold spores, no raw taters either, there is something in them that can kill a hen, if you want to know I can go downstairs and find my chicken book.
As for a treat...ours LOVE freeze dried meal worms. I can shake the bag and call "Chick Chick come on" and they come running.