Delaware State Police say 18-year-old Quatessa Ross of Wilmington was arrested Friday in the attack.
Investigators say Ross ran up to an 89-year-old woman who was loading groceries into her car Feb. 25 at a Pathmark store parking lot.
Police say Ross punched the elderly woman in the head, knocking her to the ground. Police say Ross stole the victim's waist pack containing money and credits cards and ran away.
The victim was taken to a hospital where she was treated and released. Doctors later found she had suffered a bone fracture.
Ross is charged with first-degree robbery and second-degree assault. She's held on a $32,000 cash bail.