At about 12:45 a.m., Petaluma police responded to a report of an assault at The Rocks Bar and Lounge, located at 146 Kentucky St.
Investigators were told the victim was inside the bar with two female friends, and while standing in line to use the restroom, a female suspect cut in front of the victim and then entered a bathroom stall after a verbal altercation.
The suspect then exited the stall and began assaulting the victim with a wine glass she was carrying. The glass broke against the victim's head, and the suspect continued striking her on the face and arm with the broken glass, police said.
The victim suffered lacerations to her left arm, nose and lower lip, and several contusions on her face. She was taken to a local hospital to be treated for the injuries.
The suspect is described as a white woman between 20 and 30 years old with a thin build and curly blond hair. She was last seen wearing a black V-neck top and jeans.
Before police arrived, the suspect fled the bar with a man who is about 40 years old and was described as "scruffy" and wearing a baseball hat, according to police.
The suspect may have also received a laceration to her hand during the assault, police said.
Anyone with information about the attack is asked to contact Petaluma police at (707) 778-4372.