I borrowed some books from the library for my sister; she was late in returning them and said that I shouldn’t worry, she will pay the fines. Am I allowed to take money from her for the fines, or have her pay it directly to the library, or is it considered Ribis? Is there any way she can pay it?
There is no problem of ribbis here. The reason is because there was never monetary loan here, where you borrow one thing and give back something else. Here you are like renting the book for free for the first two weeks, and after that they charge rent for it, in the form of a fine. This is not ribbis. This would not only apply to books from a library, but to any place that lends items, and they have to be returned.