My nomadic sister is visiting me in Mexico City for a couple of weeks. Her normal mode of travel involves busking (playing music and/or singing in the streets) for money. She wants to do this in Mexico City. Can she do this with a standard tourist visa? Are there any other legal restrictions on this? Is a permit needed? Are there any places where it's not permitted?
Note: I realize Mexicans do this all the time, and I would be surprised if they all have permits, but I would not be surprised if they pay off an enforcement officer if they are ever challenged. As my sister doesn't speak Spanish, this could be a complicated matter, so naturally she prefers to operate above board if possible.