Mhairi Black made the comments in the Sunday Times as the First Minister gets set to lay out the next steps towards a fresh ballot.
The SNP leadership has consistently stressed it does not support an unofficial independence vote and Ms Black has become the most senior figure to give some authority to the idea.
She told the newspaper: "There could be mileage in a consultative referendum because the Scottish question is complicated.
"The current United Kingdom government position is weak and unsustainable, and if the last five years proves anything, it proves that what happens at Westminster is unpredictable."
The MP for Paisley and Renfrewshire South added her preference would be to do the next referendum "by the book" and that an official referendum would ensure international recognition.
Scottish Conservative chief whip Maurice Golden said:“The childish behaviour of the SNP surrounding a wildcat referendum is quite astonishing.
“Fully grown men and women are having public tantrums because they aren’t getting their own way on indyref2.
“If Nicola Sturgeon is a serious leader, she should rein these people in and remind them of the law.
“The last thing Scotland needs is to be dragged back to the dark and divisive days of 2014.”