The revelation came as the former political staffer's legal team temporarily delayed Liberal Senator Linda Reynolds' bid to access documents related to the $2.4 million she was awarded in compensation from the federal government.
The former defence minister, who plans to retire from politics at the next election, is suing Ms Higgins and Ms Sharaz over a series of social media posts she says have damaged her reputation.
The senator's legal team wants to know who controls a trust they claim Ms Higgins set up to protect her compensation payment, which if true could have serious legal consequences.
They want the Supreme Court of Western Australia to set aside the trust amid fears it could prevent Senator Reynolds from getting damages if she wins the defamation case.
"There's a trust established called the Brittany Higgins protective trust," lawyer Martin Bennett told reporters outside court on Thursday.
"We'd like a copy of that trust. We don't know who the trustee is. We need to know those facts.
"We've been seeking a copy of the trust deed since March."
Ms Higgins' legal team was granted more time to comply with Senator Reynolds' request for documents.
"The judge has accommodated their request not to interfere with Ms Higgins' wedding (in early June)," Mr Bennett said.
Details of the wedding have not been made public.
The defamation case returns to the WA Supreme Court on July 17.
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