Praise be to Allah.
What the library worker did of copying the notes without the owner’s permission is a transgression and wrongdoing. It is not permissible for one who knows the situation to copy or buy these notes; if he does so, then he is a partner in the transgression and sin. Intellectual property rights -- such as written works and inventions -- are protected and belong to the authors; it is not permissible to transgress against them. For more information, please see the answer to question no. 129191
Based on that, your relative does not have the right to make use of these notes; rather she should return them to the library and get her money back. And she should advise the library worker and point out her mistake to her.
If she needs notes on this subject, she should look for them among her friends or in other libraries.
And Allah knows best.