That is good advice.
Flour never worked for me because by the time I realized the snake was missing she was already in a hiding place she liked. I suggest sitting silently with no TV, no music, no lights in the middle of the night and listening. Mine at least are very clumsy and eventually you'll hear something get knocked over or some movement that's not supposed to be there and then just follow the noise. I know you're offering heat but have you checked things that would be giving off heat on their own? Before you even set up the heat lamp she may have found a nice warm place to hide. Good luck.
JLC types faster than me lol