I know someone who came to the US (from Chile) on a tourist visa and then returned a few months later with an F-1 to study English. Her program is about to end and she would like to stay for another 6 months (the grace period after studies with an F-1 is just 2 months). Both visas have almost 10 years before they expire. Is it possible to go to Mexico for the weekend and then return to the US on the tourist visa, which would would allow for 6 more months?