Authorities had said that Maria Susana Flores Gamez was likely used as a human shield and that an automatic rifle had been found near her body.
Federal prosecutor Enrique Fedegrino said Tuesday that tests indicate there was gunpowder residue on her hands.
He said authorities are still investigating if she shot at soldiers.
Flores was crowned 2012 Woman of Sinaloa in February.
The slender, 5-foot-7-inch woman had competed with seven other contestants for the more prestigious state beauty contest, Miss Sinaloa, but didn't win.