What is the ruling on a fasting woman breaking her fast intentionally in Ramadan due to severe physical weakness, malnutrition, and her sister's neglect of her? Is this considered an excuse that permits breaking the fast with the payment of expiation, or has she committed one of the major sins?

Fasting in Ramadan is obligatory for every adult, resident, and capable Muslim. It is permissible for those who are unable to fast, such as the sick and the traveler, to break their fast. This also applies to those who are overwhelmed by hunger and thirst beyond the usual limit. So, if you are unable to move due to physical weakness, and you experience tremors and paleness, then you are permitted to break your fast. Similarly, if you are initially capable of fasting but severe hunger or thirst afflicts you during the day and makes it difficult for you to continue, then you must have the intention to fast from the night before, and then break your fast if it becomes difficult for you. In both cases, you are required to make up for the missed days in the future. You are only to resort to expiation (kaffarah) if your inability is continuous and not expected to cease.