(The news article, and to a lesser degree the study’s abstract imply females being more aggressive rather than self-reporting being so, which is what the study actually discovered.)
Females show higher sibling-specific aggression than males, study finds
In terms of direct aggression, girls and women [reported being] slightly more aggressive towards their siblings [than] boys and men. Men and boys, by contrast, [reported being] more likely to be directly aggressive with non-siblings.