The idea of 'switching off humanity' is very shady and has no particular rules.
I would say even if one's humanity is turned off, that person still knows who or what he/she is most attached to. Its like when Damon turns off his humanity, its Stefan or Elena who is closest to Damon would be able to convince him to turn it on/ bring back his humanity. Same goes for Stefan, it will be who he is closest to. If I remember correctly, when Stefan's Mom turned it off, Stefan was the one who took it upon himself to turn it back on.
There was also an idea that if you turn off your humanity and kill the one who are closest to you, then there will be no one who can make you feel again and can convince you to switch your humanity back on.
Elena has a lot of memories of her family and childhood linked with her house, burning down the house removes that from ever being used to bring back her humanity.