These details about Ernst’s wife were recently discovered by the Parisian lawyer Pascale Ernst (who is a descendant of the late C19th musicologist Alfred Ernst rather than the early C19th violinist). By looking into burial records held in Nice, she confirmed that Amélie died aged 80 on 13th November 1914. She is buried in her husband’s tomb in Nice, having outlived him by nearly 50 years. Unfortunately, there is no inscription about her on the stone, presumably because there was no relative on hand to ensure that it was done.
For more information about Pascale, Alfred and the search for Amélie, see the Questions section of this website.