In short, the FindAGrave link you are using is for another person, not the person represented in the profile. In this case, reviewing the Links to FindAGrave page, the correct way to add this type of link would be through a template:
{{FindAGrave|126495476|sameas=no}}
The sameas=no parameter tells the system that the FindAGrave profile is for another (related) profile, but is being used to provide information for this profile.
Once you add that to the profile of Clementina (Hay) Duff, you can then mark the error as Corrected!