Police say the suspect, Theresa Monique Jefferson, 33, followed another woman into the store Saturday and assaulted her, The Baltimore Sun reported.
Jefferson reportedly knew the victim, whose boyfriend has a child with Jefferson, police said.
Jefferson turned herself in after the incident and was arrested on charges of first- and second-degree assault, theft and destruction of property.
Haz mat crews were called to the scene after bystanders complained of watery eyes and other effects, Baltimore County Fire Department spokesman Glenn Blackwell said.
Blackwell said 19 people were taken to area hospitals after the incident, including one person who had a potentially serious injury.
The store was evacuated and closed for several hours Saturday until employees cleaned and ventilated the area, Walmart spokeswoman Dianna Gee said.
"This is obviously not the type of behavior that we would expect from people at our stores," Gee said. "And we want to apologize for any inconvenience this may have caused other customers."