In the case of Louisiana, they don't have "martial law", they have a "state of emergency".
In order for the US Military to assist in restoring law and order without violating posse commitatus, Governette would have to tell President Bush (and inform the Congress in writing, I believe) that a "state of insurrection" exists in Louisiana and formally request that the Federal government come in to put it down.
Governette is too busy bawling over the Oxygen network while devouring Rocky Road ice cream to do that or to even figure out what day it is.
Why should she as long as she holds back and the MSM makes the President the villian and the majority of the country hasn't a clue what the law really is.