Since she is new to your flock, she could possibly have coccidiosis, but other problems may be likely that are causing her not to eat. Dark green poops usually are due to not eating much. If she has been with your other birds, she could possibly have been kept from food and water. Feel of her crop in her right upper chest to see if it is empty, full, hard, doughy, or puffy like a balloon. Also feel of her lower belly between the legs to feel if it is enlarged compared to others. Has she laid eggs recently?
If you have poultry NutriDrench, offer a few drops up to 2 ml daily. Other electrolytes can be used. Mix a little chicken feed with water to make it wet, and add some cooked egg and offer it.