Only Geraldine Carrion and Steffy Aradillas were born in Mexico. However, Carrion, who played for CETYS in Mexicali, didn't make the final roster. Aradillas played for San Diego State, was hitless in three at-bats.
If you were watching carefully, you might have noticed that the name on the back of Brookshire's jersey was Gonzalez. Her full name is indeed Susana Brookshire Gonzalez.
O'Toole's full name is Danielle Denise O'Toole-Trejo.
My Mexican friends (one of whom played softball for U. de Guanajuato 20 years ago) aren't at all bothered by all this. I can see it both ways: sending a team of ringers to Japan doesn't do much to develop the game in Mexico. OTOH, if they didn't use the ringers, Mexico wouldn't have made the field.
But here's who got hurt from this: Puerto Rico (ranked #4), Netherlands (#10), Czech Republic (#11), and Philippines (#12) had to stay home, and one can easily argue that they were more deserving of Mexico's spot.
One more thing; I picked a few Italian players at random, and yes, they have some US born and developed players, too. For example, Emily Carosone was born in Orlando, played for Auburn. Andrea Filler was born in Fort Wayne, played for Boston College and Northwestern.