NO. It is not customary to refer to hired help or household help by ethnicity. Not at all. (South Carolinian here.) I could not believe that she typed that. It really bothered me, and honestly does not speak well of MM’s character. The ONLY reason using ”mexicans” would ever been socially acceptable would be if it was a group of people whose individual names were not known. Still, in that case, most would say “the cleaning ladies or maid”. In general, such a person as those helping around the house would be called by first name, sometimes with a ”Miss“ or “Mr” added as endearment/ term of respect. Also, don get the wrong idea about “Miss/ Mr”. Those terms are not reserved for the white boss. Again, those are words that in Southern give a connotation or respect or endearment, not necessarily power or status. So, although Paul’s friends may use Miss M and Mr Alec, Paul himself or another child most likely uses Miss for the women who helped raise him- black, white or ‘mexican’. It might be used by people for the kind lady who bakes biscuits in the church kitchen every Sunday for decades and always has a kind word for the children. OTOH, “Mr. and Mrs. then Last Name” and “Yes sir, No Ma’am” are simply names and very common, polite conversation that children are widely taught, but does not necessarily mean Endearment.