A woman may choose to get either nostril pierced. Piercing placement is a decision based on personal preference and aesthetics. There is no medical reason to favor one nostril over the other.
In Indian culture, women traditionally have their left nostrils pierced. It is believed that this piercing placement makes bearing children easier and less painful. Nose rings are seen as status symbols in India and are meant to enhance a woman's beauty.
In the United States, women pierce either their left or right nostril. Some women choose to get both nostrils pierced. If a person chooses to get both nostrils pierced, piercers recommend giving the first piercing a chance to heal before getting the second piercing.