Investigators say Yenny Leyva and an unidentified man attacked the victim on Martin Luther King Jr. Way around 2:30 am Monday.
The 28-year-old victim was hit in the back of the head with a hard object, police said. Leyva and the male suspect then took off with his bicycle.
Detectives found Leyva riding the victim's bike on 16th Street. She was taken into custody and booked into the Merced County jail.
Police are still searching for the man who was with her during the attack. Anyone with information is asked to call the Merced Police Department.