If your friend is suffering from a terminal illness and therefore unable to fast, then she has to offer fidyah by feeding a person who is poor for every day of Ramadan. If, however, she is poor and she cannot afford to do so, then she is excused. Allah says: “Allah does not place on anyone a burden that he or she cannot bear.” (Al-Baqarah 2:286)

Having said this, I must rush to add: She should pay fidyah, if in case she becomes eligible to pay.