it all depends on your needs and the quality of maid. if the maid has no heart for work but just come here to 'play', she would turn bad even though you let her day off on weekdays. There are lots of boarding houses all over the territory and they can go to these boarding houses on their day off, pick up the bad habits from others easily.
So I do believe that maids would turn bad easily if you let her day off on weekends. They also need social life. For my case, unfortunately, my maid cannot go out on weekends because of family needs. They know our requirements before they work with us so no problems. Sometimes, if we are available, we will let them go out on weekends.
even if you don't let her have Sunday off, she can still be 'polluted', e.g. when she went to the market or waiting for the school bus outside your block. it all depends on her personal quality.