Peaches Geldof Mourned by Her Sister as Her Death Remains a Mystery

By Tim Nudd

04/08/2014 at 08:30 AM EDT

Peaches Geldof was mourned by her older sister Fifi in a poignant Instagram post Tuesday, as a heartbreaking final interview with the British model, writer and TV personality also emerged. But exactly what caused her this week remains unclear.

"My beautiful baby sister... Gone but never forgotten. I love you, Peaches x," Fifi, 31, wrote of her sister, 25, alongside an adorable old photo of the two of them as children.

Peaches, who was found dead Monday inside a home in Kent, England, had recently signed on to write a column for Britain's Mother & Baby magazine, seemingly completing her transition from wild child to responsible mom.

"Becoming a mother was like becoming me, finally," Geldof said of her two sons – Astala and Phaedra, who will turn 2 and 1 later this month – in a recent interview in the magazine's print edition, according to reports in the British press.

"I felt finally anchored in place, with lives that literally depend on me, and I am not about to let them down, not for anyone or anything."

Meanwhile, Kent police are treating the death as non-suspicious, but are not releasing further details as their investigation continues. They are expected to supply a report to the coroner, and an autopsy will likely be carried out in the next few days.

• Reporting by PHILIP BOUCHER