A Sydney woman has admitted stabbing her 18-year-old sister to death in a fight over a pair of hair straighteners.

Kathleen Worrall, 20, was charged with murdering her sister Susan in their Strathfield home in October 2008.

Susan died after being stabbed in the neck.

Kathleen Worrall was charged over her death later that day and has been in custody ever since.

In the NSW Supreme Court today, she pleaded not guilty to murder.

But the prosecutor told the court the Crown was accepting her plea of guilty to the lesser charge of manslaughter.

She will be sentenced on March 26 next year.

- ABC/AAP