The sight of Prushka actually being fairly self-sufficient had perhaps made Vivienne wonder if she was really needed here... but that was discounting the fact that Prushka believed the person inside was dangerous enough to attack her, so acting as some sort of safety net was still reasonable enough.
But why risk oneself for someone's else sake? A misguided attempt perhaps at holding a friendship, a mission driven by pity rather than logic? Well, there was a degree of logic here -- if this was a local or someone privy more of the happenings 'behind the scenes' of Road's End, then ultimately this was not a vain venture.
"Be careful... I will... try not to show myself... unless you are in trouble... don't want to... startle the 'cat'..."
There was no need to agitate the person inside after all, though perhaps that their scent would be good enough to pick Vivienne's presence up -- if they were some sort of animal-human hybrid and had heightened senses, masking her arrival onto the rooftop by going up at the same time as Prushka wouldn't be that useful... but well, what else was there to do other than observe how things would play out?
As Prushka got onto the building's roof, Vivienne displayed a rather surprising competency in parkour as she ran up one of the trees next to the cabin and using the momentum from her dash launcher herself onto the top of the roof. Her landing seamless and quiet, its impact barely audible as the wooden tiles had little to no stress exerted on them -- the movement of a well trained acrobat, in the image of the most supple of felines.
Was she used to doing this?
Her eyes trained onto the window that Prushka would eventually go in, she waited, for the time to act, if that ever came.