A 27-year-old woman, whose name wasn't reported, was arrested Friday, suspected of being involved in the melee that fatally injured Pham, the Los Angeles Times reported.
Pham was hospitalized with blunt-force traumatic injuries to the head and died after three days on life support.
On Wednesday, Vanesa Tapia Zavala, 25, pleaded not guilty to murder for her alleged role in the incident. Zavala was being held on $1 million bail.
"Three people at various times, depending on what video you look at, were involved physically with Ms. Pham," Santa Ana's interim police chief, Carlos Rojas said. "While there was a physical altercation, we don't know what precipitated it."
"We don't see this as a hate or gang crime," he said.