The girl has been detained by the police.
"She has admitted to killing her 20-year-old brother-- Siddharth Dafda-- at their house in Sarvodaya Society in Amreli city," Police Inspector Ashok Pandya of Amreli town area told PTI.
The incident took place yesterday, Pandya said, adding that the accused attacked her brother with a sharp weapon and slashed his throat when he tried to escape from the scene.
"The girl told us that she killed her brother as their parents were giving him more importance," the police officer said.
Police are probing this angle as well, he said, adding that a case of murder has been filed by their father.
Further investigation into the case is on.