The Waitemata Serious Crash Unit investigation is expected to take at least several weeks.
"Inquiries into the type of licence that the driver held will form part of the investigation and police are not able to confirm anything more about this aspect at the moment," a police spokeswoman said.
Ms Baer worked for Matakana realtor Jodene Mildon and cared for her 14-month-old daughter, Lacey. She formed a special relationship with Ms Baer and described her as her "au pair daughter".
Ms Mildon said the accident had devastated the small community.
"Janine ... became like a daughter to me and had quickly become so popular within our community and everyone who met her loved her as she was such a beautiful person," she said. "We are all grieving and this is just so unfair and was just such a tragic and sudden accident."
French traveller Cindy Poncin met Ms Baer in New Zealand, and the two quickly became friends.
"We built a special link together because she was a special person. She had a such a good heart and she was so generous and had plenty of life."
On an online profile, Ms Baer described Matakana as a "wonderful small town" and posted images of her travels around the North Island, including pictures in Rotorua, Omaha Beach and at the Tongariro Crossing.
Friend Christina Piper described Ms Baer as a "bright, bubbly and responsible girl", who was "amazing" with children.
"She is going to be so missed by those that knew her, my heart aches for her family and friends back in Germany and her father who will return home to Germany without his wife or daughter," she said.
Ms Baer was close to Ms Mildon's home when the crash happened. Mrs Reinhardt-Baer was sitting in the back seat and her husband was in the front passenger seat. They were visiting from Zwenkau, a small town 200km southwest of Berlin.
Mrs Reinhardt-Baer was unable to be revived, and her daughter was airlifted to hospital.
Ms Mildon said Ms Baer "definitely" held the correct licence for driving in New Zealand.
