I give the liquid wormer orally to each chicken. That way you know each bird got properly wormed and no guesswork.
Use a syringe without a needle. Have someone hold the hen for you. Preload your syringe. Then pull the hens wattles down and her mouth will open. Quickly shoot the liquid in her...
Thanks for the pics. You're correct, tough to tell if it's a worm. It would be best to clean off the feces from her rear end and do the same for all your chickens. Feces stuck to feathers can and will attract flies and you dont want that to happen.
I use a garden hose to spray off their rear...
Worms in poultry feces are white or off white in color. I recommend that you thoroughly inspect Minnie's rear end area for fly strike/maggots.
The next time she poops, please take a photo or two of what you're seeing so we can help ID whatever it is.