A former adviser to first lady Melania Trump Melania TrumpThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power FBI director casts doubt on concerns over mail-in voting fraud Trump: 'We could hardly hear' boos, chanting at Supreme Court MORE was among those who raised concerns about supposedly excessive spending by members of the Trump inauguration committee, according to court documents reviewed by CNN.

CNN reported Thursday that Stephanie Winston Wolkoff has become a witness in the ongoing investigations into whether the inaugural committee misspent funds or accepted bribes in exchange for access to top officials.

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Winston Wolkoff reportedly received a subpoena from Washington, D.C., Attorney General Karl Racine, who requested that she turn over all documents in her possession detailing expenditures that she deemed "wasteful, mismanaged, and/or improperly provided private benefit."

In a statement to CNN, Winston Wolkoff declined to comment, citing a nondisclosure agreement that she signed upon joining the 2017 inauguration planning team.

"If the [Presidential Inaugural Committee] were to release me from this obligation, I would be able to speak freely without the fear of legal or financial repercussions. Otherwise I am regrettably unable to provide any substantive comment," she said in a statement to CNN in April.

Emails obtained by CNN indicated that Winston Wolkoff clashed with former Trump inaugural committee chairman Tom Barrack over one vendor, Hargrove Inc., which she reportedly believed was charging exorbitant prices for services.

"I am expressing my concerns because I have no options at this point," she wrote in one email, reportedly citing "many line items that were not reflected, rentals that were not sourced, budgets that were not accurate and décor elements that were not feasible."

"Stephanie was underestimated," one ally of Winston Wolkoff's told CNN. "They were hoping for a New York socialite who would not look at the details."

The White House did not immediately return a request for comment on the emails or the investigation.

The four-day inaugural celebration cost more than $27.3 million in public funds, and reportedly still had an outstanding balance of more than $7 million owed to the city of Washington, D.C., as of June.

]The total cost of the inauguration, $107 million including private donations, was more than twice as much as former President Obama's in 2009.

—Updated at 9:05 p.m.