Is it permissible to take out a loan to help a sister who is suffering from many debts and needs eye surgeries, as she can only see with one eye?

Borrowing with interest is Islamically forbidden except in cases of necessity. The criterion for necessity is reaching a point where, if one does not partake of the forbidden, one would perish or be close to perishing, such as someone who needs a surgical operation, the omission of which would lead to the loss of an organ or its function. As for merely settling debts, it is not a necessity unless the failure to settle them leads to severe harm like imprisonment. It is permissible to borrow with interest to ward off a necessity for a Muslim, for a Muslim is like one's own self. It is obligatory to commit a forbidden act or abandon a duty to save another Muslim, such such as a fasting person breaking their fast to save a drowning person, or swearing falsely to save a human being.