It all happened after the woman ran out of gas at the Southwest Freeway and Belfort.
She had two of her kids with her, her nine-year-old son and a 15-year-old daughter.
The woman ran out of gas around 8pm and called her mother-in-law for help.
Her mother-in-law arrived, went and got gas and returned.
As they were filling up the car, another car on the highway clipped a van, lost control and crashed into the family's sedan.
The mother-in-law, who was outside of the car, was killed.
Her daughter-in-law and 15-year-old granddaughter had non-life threatening injuries.
The driver of the car was taken into custody.
Police are looking into what caused the driver to crash in the family's car. null