Many workers come to Japan from the Philippines undocumented. Often times it is women involved in the sex trade, or they find work at low-end hostess clubs and 'snack' bars. Often the money earned is sent back to the home country. Not all of these undocumented workers come from the Philippines (also Thailand, other Southeast Asian nations), but in Japan, the Philippines is the country most associated with this.
Maria's character is representative of this, and is most likely Philippino, especially considering HER NAME IS FUCKING SPANISH YOU DIPSHITS