Canada

I am not a lawyer, but by my understanding, treason's pretty narrowly defined as being involved in armed insurrection, assisting the enemy in time of war, or passing official secrets to an enemy country. If Smith has done anything like that, she's managed to keep it very quiet. If she has, at any time, advocated the use of force to drive the federal government out of Alberta, she may have committed a different (also very serious) crime, sedition. I'm sure there are people trying to figure that out right now.

If she hasn't done any of that, she's in the same position as Quebec separatist politicians back in the day: stupid, misguided, and trying to harm the country, but technically not treasonous.

In the event she did hold a referendum and not enough of the remaining sane Albertans turned out to vote in it, the federal government would be best served by quietly dragging its feet on the messy proceedings required to let them leave (while pointedly going through the motions of setting up temporary border checkpoints), bombarding the population with propaganda, and hope that by the time Smith's term ends, buyer's remorse has made things swing the other way.