Fifi posted this picture to Instagram on Tuesday, which shows the two sisters - who have a six-year age gap - as young children.
Alongside the photo, Fifi wrote: “My beautiful baby sister... Gone but never forgotten. I love you, Peaches x”
The police were called to Peaches' home in Kent on Monday, where her body was discovered.
The 25-year-old lived in the town of Wrotham with her husband Thomas Cohen and their two children, 23-month-old Astala and 11-month-old Phaedra.
Fifi has another younger sister, Pixie, as well as a half-sister Tiger Lily, whose father was INXS singer Michael Hutchens. The girls’ mother Paula Yates died of a heroin overdose in 2000.
Her father Bob Geldof remembered Peaches fondly in his own emotional statement, saying: “She was the wildest, funniest, cleverest, wittiest and the most bonkers of all of us.
"We loved her and will cherish her forever.”
The last photo Peaches posted to her own Instagram page two days before her tragic and untimely passing was a picture of herself as a child with her late mother.