The Chicago Police Department said in a news release on Saturday the incident happened around 5:45 p.m. in the city's Little Village neighborhood, when 21-year-old Araceli Diaz met with the 14-year-old girl after the teenager arranged the meeting to buy a dog.
When the 14-year-old met up with Diaz, officials said the teen pulled out a pellet gun, struck the 21-year-old on the head with it and tried to take the dog without paying for it.
"We're not sure where they met initially or how they communicated, but all we do know is that the 14-year-old did show up with other intentions and she pulled out a BB gun," Chicago Police Officer Jose Jara told FOX32.
In response, Diaz then allegedly pulled out a handgun and shot the girl in the chest.
Chicago Police said in a news release the 21-year-old was found to have a valid Illinois Firearm Owner's Identification card, or FOID card, to possess a weapon, but no concealed carry license.
Diaz was subsequently arrested in Cicero about an hour after the shooting and charged with unlawful use of a weapon, according to police.
The 14-year-old was transported to an area hospital where she was treated for her gunshot wound before she was arrested Saturday morning and charged with attempted armed robbery. She is scheduled to appear in juvenile court on Dec. 9.
Chicago police said that Diaz is scheduled to appear in court on Sunday.
"A BB gun can appear like a real gun and to anyone out there it's gonna appear like a real gun, to the police, and to any individual, and if someone's carrying and they have their own CCL they may use their own gun to defend themselves," Jara told FOX32.