She doesn't understands, but she sure knows that there has been something very wrong going on with humanity.
She knew no one would come over again.
Why do you think a robot able to be so much precise would be so eager to skip her programated order to treat only the 2.500.000th visitor when he's something like one million too early?
She knew from the start that what she did was pretty useless, even if she said "I hope tomorrow, there will be visitors".
Plus, at the end, when you suppose that she will say something totally unrelated, she wonders what did go wrong with humanity.
She knew all along.