How about if you stick a sign over the top of the light switch saying "Please don't turn this off, there's an emergency with the NAS and I'll lose all the data

How about if you stick a sign over the top of the light switch saying "Please don't turn this off, there's an emergency with the NAS and I'll lose all the data if this switch gets turned off"? If she still turns it off anyway, you'd be forgiven for being a tad unhappy about it... ;)