Visible crew/equipment: After Bucho's men bring the dead knife thrower back to their ranch, when Bucho enters the limo, the boom operator and boom are visible, reflected in the limo window. (00:55:25)
Visible crew/equipment: When Salma Hayek is tossing the bullet she has just removed from Antonio Bandaras's shoulder, you can see the reflection of Robert Rodriguez holding the film camera on the metal dish.
Visible crew/equipment: When the limousine explodes (flying several feet into the air) after being hit by the second rocket, in one or two shots (most noticeable right before it explodes, during the rocket POV shot), you can see chains attached to parts of the limo, that were not there in previous shots. This has to do with the original idea, which was to have the car flip over in a deliberate direction when it exploded.
Visible crew/equipment: When Banderas and Catalina are on the rooftop, and Bucho shows up and Banderas doesn't shoot. When they start going to the next rooftop, you can see a shadow of a microphone going up the wall.
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