It was the first time the 69-year-old voted after moving to the US from China when she was about 12.
"I feel the country needs someone who is fresh in office. The government is always well-manned with lots of brains and good advisers so he'll be well-informed," she said.
"I think people are afraid that he's not a well-seasoned politician but I think as a very successful businessman he'll improve the economy and he'll shake up the system and that's what America needs right now."
On calls for tougher gun controls in the US, Ms Koo said that would be impossible because there were "so many guns" around.
"Some kind of registration and background checks- all those are fine but the authorities never talk about responsible gun owners. Controls are needed on those that are irresponsible in the use of guns."
Her comments followed reports that at least two people were injured in a shootout involving "active" gunman at a polling booth in California today.
Americans residing in Whangarei are not planning to gather anywhere to follow the polls but those who have voted will be glued to the latest TV news, particularly around mid-afternoon when the final batch of results should be out.