Well, there are many theories out there on the world wide web, about killing head lice with hair straighteners. There is no doubt if you were lucky enough to catch a head louse between the hot plates then it would most definitely kill the little critter. However, they do tend to run quite quickly and are very difficult to catch. The heated metal may also kill some viable eggs, though there would probably be more eggs left in your hair with baby lice ready to hatch than eggs killed. Which means the infestation will grow.
The main problem with using hair straighteners when you have head lice is that they will dry out the nits (white empty shells), shrinking the shells, which makes them very difficult to remove and look very unsightly in hair. When there are lots of white nit shells in the hair it can be difficult to style your hair without them being noticed especially around the ears and the nape of the neck.