Who says it isn't? And who says Brexit really is the best for the UK? We're dealing in gargantuan unknowns on both sides of the border. Nobody knows, least of all the UK government it seems...
But what do you expect her to do? Really? Sit quietly by and continue to be told what to do by Westminster? That would be a dereliction of her duty as FM. Besides, nearly all of the arguments that Theresa May is advancing for Brexit are precisely the ones that Nicola Sturgeon can use for...