What is the ruling on benefiting from money sent by a sister who works as a flight attendant, out of necessity and due to the absence of any other source of livelihood?

It is not permissible for a woman to work as a flight attendant due to the negative repercussions and Shariah prohibitions associated with this profession. The necessity that permits a prohibited act is when a woman reaches the point of perishing if she does not work in it. If your sister has lawful money other than her salary, there is no harm in benefiting from what she gives. However, if she has no money other than her unlawful salary, then it is not permissible for you to benefit from it unless you are poor and in need, because unlawful money, when it reaches a poor person, becomes lawful for them.