There was "no way" Arlene Arkinson would have willingly left home and never contacted her family, her sister has told an inquest.
Anita McGale also dismissed claims the 15-year-old schoolgirl was pregnant when she vanished in August 1994.
A visibly upset Mrs McGale, who was giving evidence by video-link from Omagh Courthouse, said: "I just know Arlene. She wouldn't have done that."
Arlene, from Castlederg in Co Tyrone, vanished after a night out across the border in August 1994. Her body has never been found.
She was last seen with convicted child killer Robert Howard, who was acquitted of her murder in 2005 by a jury unaware of his conviction for killing another teenager in south London several years earlier.
Howard (71) remained the prime suspect in the Arkinson case until his death in prison last year.
When asked by Frank O'Donoghue QC, counsel for the coroner, to comment on the theory that Arlene may have "simply left home and gone to live elsewhere in another country or another place", Mrs McGale replied: "No way."
Belfast Coroners Court heard how Arlene had lived with Mrs McGale at her home in Omagh for about 18 months after the death of her mother in 1990.
But the arrangement ended when Mrs McGale's former husband Seamus McGale was accused and subsequently convicted of sexually abusing Arlene, the court was told.
He was sentenced to 18 months in prison but was released after six months on August 4, 1994 - 10 days before Arlene went missing.
While living in Omagh the teenager would have socialised in Castlederg, but would not have stayed away without informing her sister, the hearing was told.
"She always told me where she was," said Mrs McGale.
The inquest has previously heard claims that Arlene confided in friends that she was pregnant and told others she had been treated in hospital for a miscarriage.
Mrs McGale, who described their relationship as "close", said she had no knowledge of any pregnancy or miscarriage, and did not know why her sister would have made up such a story.
The hearing continues today.