Police released pictures of the woman still being sought. They said she took several items and tried to leave the store without paying.
A loss prevention officer tried to stop her, but authorities said she kicked him and implied she had a gun, even grabbing for her waist.
The woman was able to get away from the store.
Retail theft is a growing concern throughout the Philadelphia region.
On Friday, officers from Delaware and Chester County gathered for a retail theft training session.
"We are always better as law enforcement when we partner and we collaborate," said Chester County District Attorney Chris de Barrena-Sarobe. "We have a lot of retail theft happening in Philadelphia and that is bleeding out into the counties."
Delaware State Police haven't identified the suspect who attacked the loss prevention officer and are looking for help from the public.