The passenger, Vyvianna Quinonez, allegedly punched and grabbed the hair of the female flight attendant, who lost two teeth and suffered other injuries to her face on the May 23 flight from Sacramento, prosecutors said in court documents.
Quinonez was escorted off the plane at San Diego International Airport and arrested for battery causing serious bodily injury in connection with the incident, according to the San Diego Harbor Police Department.
On Wednesday, she was charged with assault in federal court, along with interfering with a flight crew.
An affidavit filed in San Diego federal court stated the flight attendant asked Quinonez to fasten her seat belt, stow her tray table, and wear her face mask properly as the plane began its final descent.
But Quinonez, from the Sacramento area, allegedly failed to comply and pushed the attendant, City News Service reported. She later stood up in her seat and allegedly punched the attendant in the face and head with a closed fist, according to the affidavit.
The attendant suffered three chipped teeth, including two that needed to be replaced with crowns, the affidavit said. She also suffered a bruised left eye, a cut under her eye requiring four stitches, and bruising on her arm.
At the time, Southwest told Fox News the airline had been informed that the passenger had "repeatedly ignored standard inflight instructions and became verbally and physically abusive upon landing."
Images also circulated on Twitter from user MikuniTaro which appeared to show blood on the flight attendant's face.
"They started to argue and the passenger stood up and punched the flight attendant in the face and knocked her out," passenger Taro Arai, who was on the flight and witnessed the incident, told Fox News.
After she was taken into custody, Quinonez told law enforcement that she acted in self-defense, according to the affidavit.
In May, TWU Local 556 President Lyn Montgomery wrote a letter to the airline that was obtained by Fox News, which called the latest in-flight event just one of the hundreds of misconduct incidents that occurred on Southwest flights in the weeks prior to the incident.
"I write to you today because we cannot tolerate our beloved cohearts being abused in such a manner, and because I am asking for your help and leadership in ending these travesties," the letter said.
The union said there were 477 incidents on Southwest from April 8 to May 15.
Quinonez is scheduled to appear in court in San Diego on Sept. 17.
She also faces charges in state court.
Fox News' Daniella Genovese and The Associated Press contributed to this report.