Prosecutors say she did it because the 17-year-old had a disagreement with her son.
A Kane County judge returned the guilty verdict for Timera Branch Thursday. Branch's teenage son faces a separate murder trial in the death of John Keyes III.
Timera Branch was found guilty on two counts of first-degree murder by Associate Judge Allen Anderson.
She faces a sentence of between 20 and 60 years in the Illinois Department of Corrections, and she will be required to serve 100 percent of her sentence.
"My first reaction is to thank the Lord and the prosecutors, detectives, judge and everyone who helped to get justice for my son," said the victim's father, John Keyes.
The judge stated he was convinced that Timera Branch intentionally ran down Keyes III on Nov. 8, 2009 and pinned him against a brick wall with her vehicle, crushing him. She then exited her car and incited others in a second car to continue the attack.
"We're pleased today with the decision of Judge Anderson, finding Timera Branch guilty of both counts of first-degree murder," "It is this type of vigilante justice that has no place in civilized society."
Branch's attorney Liam Dixon did not talk on camera, but released this statement: "The initial reaction is disappointment. She was not trying to deny her guilt. She never intended for this tragedy to happen."
"My son is going to always be right here with me, so, I feel... much better that I know that the person who did that to my son is gonna pay for it, but at the same time... closure - I don't know," said the victim's father.
The prosecutors argued that branch wanted to show her son, Lacorbek Benion, to stand up for himself, because he was constantly bullied.
The two teens fought over a girl the night before the incident.
Benion, 17, is accused of taunting Keyes III as he was pinned against the building and striking him with a bat, causing his death. Benion also faces first-degree murder charges.
The courtroom was packed with members of Keyes's family.
It gives me closure to know that we got justice," said Keyes's sister, Deandra Keyes.
The judge rejected the state's request for an extended sentence.
"Of course, we would have wanted to get the extension... but, I don't know, the judge didn't see it that way," said the victim's father.
Branch remains in the Kane County Jail, where she has been held since her arrest. Bond was revoked upon conviction.
Benion is at home under house arrest.
Branch's next court appearance is September 28th, for post-trial motions and sentencing.