Ribbon snakes can sometimes be converted to dead fish. If you can find frozen silversides (arctic pond smelt - safe fish) sold as food for carnivorous fish, they are whole, safe, and nutritious. Not only that, they look somewhat alive if you wiggle one on the end of the tongs. Some ribbon snakes will take them with a little coaxing. If you can get her to take those regularly, you can try scenting a pinky and wiggling that in front of her.