I understand where Shirai is coming from by not wanting to tell the girl where she can get a higher quality second hand insert. If she cared about reimbursing the library with a good quality product she would have found a better alternative to the one she knows is bad but brought anyway.
Since they found a good replacement online rather quickly, it shows that if she had put in the effort it would not have been too hard. Getting her to buy them a new one at this point is a matter of principle now, because they know she couldn't be trusted to act in good faith the first time round. And in turn it allowed her to see the error in her ways (even if it was only briefly and had to be explained to her).