Bathing In soapy water removes the oils that are important in keeping their feathers water proofed. Have you cleaned out the cooped since your duck died? It looks like she has a case of bumble foot. I’d treat that right away. I believe @casportpony said not to use Vaseline in or around this area because it is petroleum based. And can harbor bacteria. Can you please get a better view of that place on her foot that looks like bumble?