The Turnbull government has thrown former Greens senator Larissa Waters a curveball in backing her in the High Court case over her eligibility to have been in parliament.
The government has filed its official submission on the seven federal politicians who have been referred to the court over their citizenship status.
It argues only One Nation's Malcolm Roberts and former Greens senator Scott Ludlam were wrongly elected, while the Nationals' Barnaby Joyce, Fiona Nash and Matt Canavan, crossbencher Nick Xenophon and Ms Waters should not be disqualified
Under section 44 of the constitution, "a subject or a citizen ... of a foreign power" cannot stand for parliament.
Ms Waters resigned in July upon discovering she still had Canadian citizenship.
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"Who expected (Attorney-General) George Brandis to be in my corner?" she told Sky News on Thursday.
She was still certain she had done the right thing in resigning her seat, saying the legal advice she received had been very clear.
"But we'll see whether the court agrees with the government's view that ignorance is somehow an excuse," she said.
"It's a pretty unusual interpretation of the constitution and I think it would probably be pretty unlikely that the court will agree."
Ms Waters could return to the Senate's red benches if the High Court agrees with the Commonwealth and she is nominated to replace herself by the Queensland Greens.
She says all the party's members know she is "super keen to go back to doing that role".
The matters will go before the full bench of the High Court on October 10.
