"I would urge her to come forward to provide information to police," Lt. Gen. Prawut Thavornsiri told reporters without elaborating.
Earlier, two men captured on surveillance video entering the shrine ahead of Monday's bombing turned themselves in, but it does not appear they're linked to the attack, Prawut said.
The men -- a tourist and tour guide described by the colors of the shirts they were wearing at the shrine: white and red -- were taken to metro police headquarters for interrogation, said Col. Decha Promsuwan, a police official in Bangkok. They both had been sought by police but have denied any connection to the alleged bomber, he said.
Later, Prawut told reporters it was unlikely they were involved in the blast.
At least 10 people may have taken part in the bombing, but the attack is unlikely to be linked to international terrorist groups, Thai authorities say.
Police have singled out one main suspect, describing him as an unidentified foreigner who was caught on surveillance video hiding a backpack under a bench at the shrine
minutes before the bomb detonated.
Royal Thai Police Commissioner Gen. Somyot Poompanmoung said Thursday he believes "several teams" were involved in the preparation and execution of the attack, which killed at least 20 people and wounded more than 120.
"This operation was carried out by a big network," he said.
"There must be a preparation for materials and explosives," Somyot said. "There must be people who scout the route. There must be people who survey the site, people who would cover and look after the bomber. There must be people who know (the) escape route and take the bomber to do it."
Even though police say at least one foreigner may have been involved in the attack, the operation is unlikely to be linked to international terrorism, Col. Winthai Suvaree, a spokesman for Thailand's ruling military junta, said Thursday.
There has been no claim of responsibility for the bombing. Thai authorities haven't said what they think the motive for it might have been, other than making vague references to unspecified people or groups who want to hurt Thailand's tourism industry and economy.
Information shared with Interpol
Thai security forces are sharing information with Interpol, the global police organization, and with intelligence agencies from allied countries, officials said.
At this point, they don't know if the main suspect is still in Thailand, said Prawut, the police spokesman.
He said investigators are reviewing surveillance video from Bangkok's two international airports as well as from the scene of the bombing.
Police have released a sketch of the suspect, showing a dark-haired man with glasses and light facial hair.
Police on Thursday doubled the reward for information leading to the suspect's arrest to 2 million Thai baht ($56,000), according to the government-run National News Bureau of Thailand. They raised it further Friday to 3 million baht ($84,000), Somyot said.
A Thai motorbike taxi driver who believes he picked up the suspect shortly after the blast said he did not seem to be Thai.
Driver Kasem Pooksuwan told CNN the man didn't speak to him but showed him a piece of paper with the name of a central city park written in English. He spoke an unfamiliar language on his cell phone during the short ride, he said.
"When I dropped him, he still appeared very calm, just like (a) normal customer. He seemed not in a hurry at all," Kasem told CNN.
Police say they have questioned the motorcycle taxi driver but haven't provided details of what he told them.