What is the ruling on a mourning woman who suffers from an eye allergy using kohl made from stone?

A woman observing the 'iddah (waiting period) after her husband's death must avoid adornment, such as kohl, throughout her 'iddah, based on the Prophet's (peace and blessings be upon him) statement "No" to the woman who asked him about applying kohl to the eyes of her daughter whose husband had passed away. However, she is permitted to use kohl for medicinal purposes at night, provided she removes it during the day.