If it was filled with smoke to the degree that you couldn't see the stairs directly in front of you, how would you see the dog or the blind guy being pulled by him? Not to mention if the stairway was pitch black with smoke there's no way anyone is walking down dozens of floors worth of stairs without respirators. Not to mention the convenient thing about stairs is you kind of don't need to look for them. I'm not trying to be obstinate but I feel like someone just added something to this story that wasn't really a factor.
And if she somehow is still alive after over two decades, may she pass peacefully to doggy heaven.