I'm so sorry about your dad. I had a chicken get very ill the day my dad passed and was determined to save her because I couldn't save my dad...so I completely understand how you feel. The only thing I can think to suggest is to see if you can find a vet to run a fecal sample. Some vets (even tho they don't treat chickens) will do this for you. Does her poop look normal? Does she fill her crop like her hatch mates? Providing additional protein with boiled chicken, fish , yogurt may be helpful as well as vitamins in her water. Fingers crossed for you.