The toddler was in the care of babysitter Karen Nenite De Luna when she was injured.
De Luna left New Zealand "within months" of the incident.
Police charged her with murder late last year and a warrant was issued for her arrest.
Detective Senior Sergeant Stuart Harvey said Bea's family have been kept up to date with the investigation and charges.
"De Luna left the country within a few months of the incident," he said.
"Police last had contact with her July 2016."
She is believed to be in the Philippines.
"Police are taking measures to get her to return to New Zealand," said Harvey.
The Herald has sought comment from Bea's parents Margie and Benedict, who now live in Australia.
While in De Luna's care, Bea suffered a seizure and was rushed to Invercargill Hospital.
Several days later her family chose to end her life support, and the little girl died.
It emerged she had suffered a skull fracture that is alleged to be non-accidental.
Fairfax reported that De Luna, who has her own small children, was interviewed by police soon after Bea's death.
She was then allowed to return home to the Philippines with her husband several months later.
The murder charge was laid in December.
In an email sent to the Daleons, published by Fairfax, Harvey said:
"We are looking at contacting authorities in the Philippines for assistance, but the information I have is that this will be a very difficult process to undertake.
"Rest assured that I have not given up on the case.
"I will continue to work through every possible avenue to bring Karen home to face the charges."
Harvey told Fairfax he was working "on a diplomatic level" to locate De Luna.
There is no extradition treaty between New Zealand and the Philippines.
While authorities here can make an extradition request, their Filipino counterparts would not be obliged to surrender De Luna.
