Nadene Lomu is driving a $75,000 Porsche - at the same time the trust set up in her husband Jonah's memory was in London trying to raise money to help the couple's sons.
The purchase of the Porsche, on finance, has caused concern among those involved in efforts to provide for the boys' future.
A spokesperson for the trust assured the Herald on Sunday that none of its funds were used to buy the car, but acknowledged the "perception issue".
The spokesperson said the trust had been aware of Nadine buying the car, but added the family had relocated and divested itself of other vehicles since Jonah's death, and had also received a "favourable deal"on the Porsche.
In a statement to the Herald on Sunday, the trustees said: "The trustees emphasise that the Jonah Lomu Legacy Trust was setup to honour Jonah's legacy and provide an option for those who wish to contribute directly to the welfare, education and pastoral care of Jonah's boys, Dhyreille and Brayley.
"The trust is independent of the family members and their personal affairs."
A fundraising dinner held in London last month raised at least $170,000. The money is intended for the Jonah Lomu Legacy Trust, which was set up to provide for Jonah and Nadene Lomu's sons Brayley and Dhyreille when it emerged their rugby superstar was broke when he died a year ago.
The existence of the financed Porsche had struck those close to the trust as unusual although the efforts of those involved continued to remain focused on the couple's sons.
The legacy trust was set up by the group of friends and supporters to raise funds for the boys.
It has so far been called on to help pay school fees and for clothing.
Nadene Lomu did not respond to requests for comment.
She also did not comment about a move by a company she controls - Jonah Lomu 7One5 Ltd - to register a trademark strikingly similar to those Jonah Lomu left to their sons.
Lomu's will revealed the star had tried to provide for the boys' future by leaving his rugby legacy to them - including trademarks - through a company called Stylez Ltd, to be administered by lawyer Chris Darlow until they became adults.
Stylez Ltd is the registered owner of trademarks and also - at the time of Lomu's death - owned a property in Wellington.
Lawyer Chris Darlow was appointed executor of Jonah Lomu's will by the All Black great.
He said he was aware of moves by Nadene Lomu's majority-owned company to register a trademark close in appearance to the branding he is obliged to protect for the benefit of the couple's sons.
"I'm going to be talking to her and her lawyer about that. The application has only just been made. There's time for an objection notice to be filed. If I have to, I'll file a notice."
Records held by the Intellectual Property Office of New Zealand show Jonah Lomu 7One5 Ltd had applied to register a similar trademark.
Earlier this year, Darlow was forced to take action after shares in Jonah Lomu's company Stylez Ltd were transferred by Nadene Lomu to give herself majority ownership. They were later transferred back.
Nadene Lomu was Jonah Lomu's third wife. The pair met in 2008 and married in 2011.
he London fundraising dinner came after struggles to raise enough money locally to help the boys.
One of the trustees, David Jones, told the Herald last month: "There's not a lot there at the moment. We didn't raise hundreds of thousands of dollars in New Zealand."