Kestra Troi was a half-Betazoid, half-Human female, born in 2330 on the planet Betazed to Lwaxana and Ian Andrew Troi. Kestra was the older sister of Deanna Troi. Shortly after Deanna's birth in 2336, Kestra was picnicking by Lake El'nar with her family and their dog. When Lwaxana looked away for a second to tend to Deanna, the dog and Kestra ran off. Kestra fell in the water and drowned.
The memory of Kestra's death was so traumatic to Lwaxana that she buried it deep inside instead of dealing with it. She even destroyed everything that was a reminder of Kestra, but Mr. Homn secreted away a picture of her in case Lwaxana wanted to remember her in the future.
When Lwaxana became pregnant in 2372, the thought of losing her child to the Tavnian culture made her depressed, stirring the pain of Kestra's death. She would later confide to Odo that the losses of her parents, sister, and husband did not compare to the loss of Kestra. (DS9: "The Muse") After marrying William Riker, Deanna would name their daughter Kestra Troi-Riker, after her. (PIC: "Nepenthe")