Billie-Jo Jenkins "flirted" with her foster father in the months before her death, the Old Bailey has been told.
Billie-Jo was found battered to death at the family home
On Friday, the court was shown a police note which detailed the concerns of one of Sion Jenkins' natural daughters.
In it Mr Jenkins' former wife, Lois, told police Annie, then 12, felt her father preferred Billie-Jo to her and the 13-year-old flirted with him.
Mr Jenkins, of Lymington, Hampshire, denies the murder of his foster daughter in East Sussex in 1997.
Lois Jenkins, 44, who has four natural daughters with Sion Jenkins, was giving evidence for a second day after flying in from Australia for the second re-trial of the defendant.
Sion Jenkins has remarried since divorcing Billie-Jo's foster mother
She and her children set up home in Tasmania after she separated from him.
The police note from July 1997 read: "She (Annie) discussed with Lois that Sion preferred Billie-Jo to herself and the fact that Billie-Jo flirted with Sion."
Lois told the court on Friday: "I don't recall her saying it in that situation but there was a whole guilty thing and that was part of it - but I don't recall her telling me specifically."
She had already told the court that Billie-Jo was beginning to "use her femininity" to get her way with her husband and other men.
Mrs Jenkins described the day of her daughter's death - 15 February 1997 - as a normal family Saturday.
She had been shopping with her two youngest daughters until her husband phoned to say that something had happened to Billie-Jo.
"As I got to the top of the steps there was a policeman standing there. He was young. He had tears rolling down his eyes.
"There was a horrible silence and everyone was still. I just knew Billie was dead," Mrs Jenkins said.
The prosecution claims Mr Jenkins hit Billie-Jo several times with a metal tent peg while she was painting the patio doors at the house in Lower Park Road.
The trial continues.