In the late spring of 1851 Dubb had accompanied her father, mother, sister and brother on a holiday trip to Germany. On 16 June 1851, she set out to record landscape views of the Rhine river. When she did not return for supper that evening, the police were called and—it is said—they combed the entire area. However, no trace of her could be found and eventually her grieving family returned to Scotland.
In 1860 the ancient tower of Lahneck Castle was to be repaired. The workmen came upon a skeleton inside the top of the ruined tower. Along with the bones, they found pages of a sketchbook owned by Idilia. On the pages, she had recorded the horror of her final days. She wrote that she had managed to climb to the top of the tower on the rotted wooden stairs. When she reached the top of the tower, however, the stairs collapsed and she was trapped. Idilia was confident that people would see her signals for rescue. As she waved from a window, the boatmen waved back.
With no one to rescue her, Idilia slowly starved. In her final hours she determined to leap from the tower, but she did not do so.