"And I'm pushing back against the racism that arose by something as beautiful as te reo Māori," she said.
Ardern said she would let Cabinet Office make the call on whether Davidson should remove the post, but "it would be the most advisable way forward, just to be really clear and not be seen to be promoting products".
Davidson said she would take any guidance on board, but there was an "incredibly ignorant pushback" on social media about the chocolate and leadership was needed.
After earlier saying she would not delete the post, Davidson later edited it - removing the reference to liking Whittaker's.
"Leeeeeeeets try this again," the edited post read.
"F**ken don't even like this flavour. But love Te Reo Māori."
Davidson said her father, Rawiri Paratene, had stood on the steps of Parliament 50 years ago to deliver the petition to make Māori an official language, and she would continue to support those who fostered that.
The Cabinet Manual stipulates "no Minister should endorse in any media any product or service".
However, it says they may appear in advertisements or announcements which were "in the public interest (promoting, for example, water safety), where no fee would be expected or accepted".
Ministers often promote New Zealand and its goods overseas – such as export products - and the Prime Minister is often gifted or loaned clothing by New Zealand designers such as Juliette Hogan, although she does not directly promote them.
Ardern said while it was clear Davidson's intention was to promote the use of te reo Māori "we do have rules which are very clear around ensuring you're not seen to specifically endorse particular products".
She said she had asked the Cabinet Office to speak to Davidson about how those rules applied and would issue a reminder to other ministers.
Asked what her own view was of companies using te reo Māori in branding, Ardern said it was an example of a company "embracing what is great about New Zealand".
"I think it's all part of our growth and evolution as a country."
