1. Determine your ability and willingness: Sister needs to consider whether she has the ability and willingness to borrow money from her brother-in-law. If not, she can politely refuse or offer help in other ways, such as providing physical support or helping her brother-in-law borrow money from others.
2. Rationally analyze the reasons for the brother-in-law's borrowing: If the elder sister is willing to borrow money from the brother-in-law, it is necessary to rationally analyze the reasons and purposes of the brother-in-law's borrowing, and whether the brother-in-law has the ability to repay the loan on time to avoid family conflicts caused by the borrowing problem.