Yes she could have swallowed hardware. That is common around chicken yards, and there is a hardware disease that can happen. Her crop appears large in the picture above. A crop disorder such as impacted or sour crop could have been possible. Have you wormed your chickens, and do you provide poultry granite grit to help with digestion in the gizzard? Necropsies can be very inexpensive in some states, especially if you tell them it is a backyard bird, and take the body in yourself.