It has also ruffled feathers because she has leapfrogged up-and-coming MPs Stuart Nash (Napier) and Chris Hipkins (Rimutaka), who are standing in blue or marginal seats, and Phil Twyford (Te Atatu).
She has worked in the Labour machine for 10 years, having studied politics and Maori - her estranged father is Maori and she is Tainui - at Victoria University.
Her colleagues call her feisty, a label she's comfortable with. "If I think something is unjust, I won't let it slide."
On Labour's chances: "Good. If you don't have faith in your party to win, you've given up before the fight has started."
On why its policies seem popular, but not the leader: "We need to do better [as a party]. And when the campaign starts proper, he'll connect with more Kiwis."
Mrs Mahuta-Coyle's not afraid to go against the party line. She believes Labour's foreshore and seabed solution in 2004 wrongly denied Maori their day in court.
She defends free trade at first, but says she would not sign an agreement with India unless it guaranteed labour standards.
"They call it child labour. It's child slavery. If that happened here, we would be outraged."
Brought up in Huntly by a solo mother, she was the eldest of three children whose world view was shaped by their poor upbringing.
Her goals are improving the lot of Maori in small communities, better mechanisms for collecting child support, and helping to educate sole parents so they can lift themselves out of poverty.
"We don't help sole parents enough. We call them beneficiaries, we tell them they're wasting their money on booze and cigarettes - that's only a small number giving everyone who's just trying to feed their kids a bad name.
"One of the keys to unlocking Maori youth potential is going into those communities and showing them more. If I wasn't shown more, I'd still be in Huntly."
Mrs Mahuta-Coyle has moved to Tauranga, where she will struggle to win the seat off National MP Simon Bridges, who has a majority of 11,742. She says she will remain in Tauranga if elected on the list.
She doesn't see herself as an MP for life.
"The most effective MPs are the ones who come in with a cause, and as soon as you achieve them, you leave for someone with different causes and goals."
Deborah Mahuta-Coyle
* Age 30.
* Labour candidate for Tauranga.
* No 26 on the list; will be an MP if Labour wins 30-33 per cent, depending on how many votes are "wasted".
* 10 years working for Labour, including in the offices of Helen Clark, Parekura Horomia and Phil Goff.
* Described as feisty, not afraid to call it like it is.
