For a binding independence referendum to go ahead, Westminster must issue an order in council temporarily devolving power to the Scottish parliament to authorise it.
But when asked if holding an vote without UK Government agreement was a possibility, Ms Sturgeon said: "I will consider what options I have if I have to get to that point". She said the SNP was seeking to exploit Brexit to pursue its "obsessive" preoccupation with independence.
Speaking on Tuesday, the Scottish government's Brexit minister, Michael Russell, said there would be "absolute clarity" on its position on European Union membership by the time of any second referendum, asking for "patience" in the meantime.
"It's putting her at odds with the democratically expressed will of the Scottish Parliament - and that should not be a comfortable place for her to be". May described Brexit as a moment of opportunity to shape a brighter future for Britain and "ask ourselves what kind of country we want to be".
In her closing address to the SNP's spring conference in Aberdeen, Ms Sturgeon will attempt to rally supporters and persuade Scots that her plans for a repeat of 2014's vote are both necessary and realistic.
"Now they apparently say, as an independent Scotland they would no longer seek to become a member of the European Union after a vote for separation - it's muddle on muddle".
Mrs May will stress that the break from Brussels will require "one United Kingdom, all pulling together to get the best outcome".
As things stand, and we have yet to hear Ms Sturgeon's conference speech - that comes tomorrow - the battle is for public opinion.
"We are four nations, but at heart we are one people".
"If a majority in the Scottish Parliament endorses that position, the Prime Minister should be clear about this". I don't think that would be fair.
The bill was passed Monday by Parliament but needed royal assent to become a law.
At a time when Scotland is falling down the global education league tables, when hospital waiting lists are lengthening and when powers to redistribute wealth and opportunity more equitably remain unused, most Scots feel that there are better ways for the Scottish government to spend its time. Using one set of arguments to explain why Brexit will be a triumph - and then the opposite to explain why Scottish independence will be a disaster.
Christian Allard, a French-born former SNP MSP and candidate for the forthcoming local election, said: "A Tory prime minister didn't want me to vote in the referendum a year ago, this one doesn't want me to vote in #ScotRef, quelle surprise!"
While further comment must await developments in the intervening fortnight ~ till the end of March ~ the government can not but be unnerved by Ms Sturgeon flagging the demand for a second vote of Scottish independence. after voters in Scotland had opposed Brexit on June 23 a year ago. Now she has changed her mind and appears to be trying to engage in some kind of horse-trading with the UK Government.