Your instincts and common sense seem spot-on, and as long as you continue to learn all you can while continuing to trust your intuition, Nubz is going to be fine. It is true that her remaining healthy stump will be most suscetible to infection after the necrotic foot falls off and leaves remaining healthy tissue exposed. But you will be surprised at how quickly a protective scab (eschar) grows to cover it. Should only take a few days. During those first few days is also when it is most advisable to loosely cover the remaining open wound and not allow the stump to get dirty or wet. If you decide to give antibiotics during that time, cepahalexin is a good antibiotic to help skin, tissue and bone infections heal. But as long as you continue with your current level of care, antibiotics will probably not be necessary. The auto-amputation process does an amazing job of keeping viable remaining tissue healthy while it prepares the necrotic foot to separate and fall away.
You probably aren't getting any responses from online vets because they aren't experienced in treating chickens and other birds, and cats and dogs rarely suffer severe frostbite. Unfortunately, birds with severe frostbite appear regularly every year on this forum, and the medical experts here are very experienced in giving poultry owners excellent advice to help their birds recover. You will receive much helpful advice here to help Nubz, so never hesitate to ask.
