What is the expiation for not performing prayers for 20 days?

A woman is permitted to work outside the home, provided she adheres to Islamic guidelines. The questioner's sister's husband should help her with household chores if he cannot provide a maid, following the example of the Prophet (peace and blessings be upon him) who used to assist his family. The questioner's sister must repent to Allah for abandoning prayer and make up for what she has missed. Prayer is the pillar of faith and does not fall away due to busyness or illness. Regarding one who abandons prayer out of negligence, it has been said that they commit an act of disbelief.