Thank you all for your advice.
Almost 10 years later, this duck (A Rong) is still alive, along with her 12 year older sister. They are very happy everyday.
This Sunday afternoon, a fox got her. I saved her from the fox but she was badly injured. Her lower back had a very big wound and most of the skin was gone. All vet emergencies were either not open or fully booked. I used Bactine and the bleeding stopped.
Monday morning, I took her to the vet for an emergency appointment. He cleaned up the wounds, put some NEOMYCIN/TETRACAINE powder, prescribed some antibiotic, pain killer, and the powder. We are giving the antibiotic every 12 hours and the pain killer once a day, and the powder as needed if the wound shows wetness.
She is improving, taking some water, a few peas, but not eating solid foods. It is about 48 hours since she ate. So we are back to this big concern: nutrition during her recovery.
She is very alert. Yesterday I dug about 10 earth worms from the backyard and she ate them in seconds! It is not easy to find earthworks in the summer.
I still believe in miracles and hope she will survive this fox attack.
Any advice is appreciated. Thank you!