Dinah Jane has Tongan links through her mother; but is also of Fijian, Samoan and Danish heritage.
She will sing at what is expected to be one of the biggest games of the tournament to date, as Mate Ma'a Tonga take on England at Mt Smart Stadium on Saturday.
Members of Fifth Harmony visited New Zealand last year. Dinah Jane took that opportunity to make a trip to Tonga to see family members.
She is among several international celebrities who have supported competing teams over the past few weeks; including Gladiator actor Russell Crowe, who tweeted a message of congratulations after Tonga's stunning win over the Kiwis just over a week ago.
The star made a name for herself as a 15-year-old after auditioning on the The X Factor USA, in 2012, where she performed Beyonce's hit: If I Were A Boy.