You will notice that virtually every middle-class apartment that was built up until the 1990s has a bedroom and separate toilet for the live-in housekeeper. This is true even for apartments in mid middle-class neighbourhoods such as Caballito (if the apartment was devised for a larger family), but probably not for lower middle-class neighbourhoods like San Cristóbal or San Telmo. In higher-middle class and upper-class areas like Belgrano or Recoleta, even smaller apartments with just 2 bedrooms generally had an extra bedroom and bathroom for the housekeeper.
I grew up upper middle-class in the 90s and we had a live-in housekeeper from Monday to Saturday. Almost everyone I knew had one, but my friends/classmates who were mid or lower middle-class "only" had someone who'd go in every day but not sleep in. Some of them perhaps had someone who'd come in a couple of days a week, but no one did their own housekeeping.
Things have changed in the last 20 years and live-in maids are now only for the super rich (mostly in barrios privados), the rich have someone who comes in daily, and the rest of the middle class generally have someone who comes once a week (or twice if you have children) for a few hours.
Even people who are now financially lower class but "mentally" still middle class go to great lengths to keep their maids. It's a hard-to-break habit.