Thanks for the information all! The link confirmed much of the info that I found at other websites and also my correspondence with her international student office on campus. Everything seems to be in order (I-20, I-94, passport, travel to approved country-Mexico, and approved islands-Jamaica, Grand Cayman). My main concern was her single entry visa has expired and is still usable because of the annual renewal of the I-20. However, it appears that this is a common situation for students and that the automatic visa revalidation occurs upon reentry. Still a cause to be nervous for someone as particular (neurotic) as myself!