Jamilah Mahan was charged with first-degree murder and aggravated domestic battery for allegedly fatally shooting Jihad Mahan, 23, at 16W630 Mockingbird Lane, the sheriff's office said.
She's been remanded to a mental health facility after a bench trial. The case will be back in court in November.
Mahan allegedly shot her twin brother before engaging in a physical struggle with her mother, police said.
"The senseless act of domestic violence alleged in this case has a serious impact on the entire community. To Jihad's family and friends, I offer my sincere condolences and wish them strength as they mourn the loss of a family member and come to terms with another family member accused of his murder," DuPage County State's Attorney Robert Berlin said in a statement.
Mahan was held at the DuPage County Correctional facility until her trial.
You can contact the Illinois domestic violence hotline at 1-877-863-6338 click here for more information.