Lupita is holding a Mexican Guitar, the 5 String Vihuela.
Although the Mexican vihuela has the same name as the historic Spanish plucked string instrument, the two are distinct. The Mexican vihuela has five strings and a vaulted (curved) back. The Mexican vihuela is tuned similarly to the guitar. The difference is that the Vihuela is tuned an octave higher than a guitar thus giving it a tenor sound or a higher pitch.