Continuity mistake: In the bar gunfight scene (where Cheech is the barkeep), Banderas and the bookie from the back room end up on the bar with pistols pointed at each other. Banderas puts his weapon down, then two camera cuts later he puts it down again.
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Continuity mistake: During the shootout at the Tarasco bar scene, there is a part where El Mariachi is shooting bad guys from the front of the bar. He switches from sitting to lying almost face down throughout the scene. (00:32:00)
Answer: Having a tough-looking, silent henchman/henchwoman is a pretty common trope in action movies. She's basically there to look tough and mysterious. I wouldn't read into it more than that, especially given how minor the character is. (Minor enough that I had to Google her, because I couldn't even remember her, and I've easily seen this movie a dozen times over the years).
TedStixon