Isabelle Welsh suffered multiple injuries in the weeks before she collapsed with a fractured skull at her home in Thornaby in September 2025, Teesside Crown Court had heard.
Alexandra Walker, 25, and her partner Harrison Simpson, 22, were both found guilty of murder and child cruelty, with Simpson also convicted of sexual abuse of a child.
Prosecutors previously said the couple, who began a relationship in June 2025, were both responsible for a "wicked" campaign of sexual abuse and violence against Isabelle.
Walker and Simpson blamed each other for the girl's injuries and suffering.
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