"At least nine or 12 shots and then everyone started running," a person who was inside the store at the time of the shooting told Channel 11.
The 25-year-old victim is in critical condition.
Alston, of Penn Hills, is charged with criminal attempted homicide and aggravated assault. She's described as a black female, 5 feet, 6 inches tall with a medium build.
The store was on lockdown for hours and was still closed as of 10 a.m.
A Walmart spokesperson told Channel 11 the store should reopen by Saturday afternoon.
“Our thoughts are with the victim and her family. We are working with law enforcement to provide any assistance we can as part of the ongoing investigation, as well as performing a review of our own,” the spokesperson said.