The incident began when one of the victims, the daughter, heard one of the suspects cough, and told her to cover her mouth when she did so, according to a police report. That led to a brief, heated dispute.
The two victims then went into the Lane Bryant store in the 2400 block of Stoneridge Mall Road.
A few minutes later they were attacked from behind by one of the suspects, who used her cell phone to repeatedly strike both victims in the head after knocking them to the ground.
The second suspect took a pair of black Ray-Ban sunglasses valued at $200 and both fled. Neither victim was seriously injured, and both declined medical treatment.
The suspects are described as Hispanic females. The attacker is described as being in her 20s, about five feet four inches tall and about 120 pounds. The woman who stole the sunglasses is described as being in her 50s or 60s, about five feet two inches tall and 160 to 170 pounds.
The investigation into the incident is continuing. Anyone with information is asked to call Pleasanton police at 931-5100.