There is a notation on one ancestry tree as follows:
At the wedding of her nephew, Henry Berthelot, son of Urbain Berthelot and Louise Fontenot, April 23, 1778, Marie Louise Fontenot Brignac signed the marriage document as the aunt of the groom. p. 10
Louise Fontenot, born in Alabama 1726, married Louis Urbain Berthelot, a French soldier. Louis was probably a son of Urbain Berthelot and Marie LeMire. He was discharged January 1, 1754 and the couple continued to Live near Fort Toulose ... " p. 47
(Source: The Brignac Family and Their Relatives in Louisiana by Janice Deitch Young, http://books.google.com)
So it appears they were indeed two different women. It would seem they are sisters despite the similarity of names (Marie Louise vs Louise). It is no wonder researchers are getting confused.
First husband's full name is given as Jean Louis Urbain Berthelot by one Ancestry researcher.