Well it's something in the larger scheme "going wrong " death is natural it's just another part of life , its outside your control , its not like you are choking the ducks to death with glee snd saying woops they died , your doing what you can to be humane a peacefull and offering comfort to the pair of ducks, so it may hurt to have to tell your friend about her ducks, you are doing out of love and basic fairness , you wouldn't want her returning to find out surprise two of your ducks passed on, so like I say it may feel wrong but it is not it's natural , its just not something we humans feel comfortable at delivering bad news especially when it comes to something involving permenant loss , you are faithfully doing your duties of a house sitter and friend to both your friend who owns the property and her ill ducks , if it was me i would be glad that i left things to you because you are doing the job well , so pat yourself on the back for doing a great job .