This really depends on what you formally agreed upon employment. It’s better to set this straight upon hiring to avoid any confusion and conflict later on. The most common practice is a once-a-week, whole day off, while others prefer once every two weeks, overnight. Whether this would be on a weekday or a weekend should also be discussed between you and your yaya.
According to the Labor Code, the law requires you, the employer, to pay the yaya’s pro-rated daily wage. However, if the yaya leaves without a justifiable reason, she forfeits any unpaid salary of work done for not more than fifteen days.