A friend recently confessed to me that she plagiarised a part of her thesis which was submitted to graduate with honors from her undergraduate university. She graduated a few years ago. Her thesis was in biology, and the part of the thesis in question is the materials and methods section. She told me that her group had used the same non-human primate model for many projects, so she decided to use the same wording that her group had used previously. She says that is was classic copy/paste plagiarism, but she thought is was okay since it was "just methods which are the same in every project." Her thesis was about 50 pages, and about three pages were plagiarized. The rest of the thesis is her own work (introduction, results, discussion, etc.). While any plagiarism is bad, is this cause for worry? I want to reassure her since methods seem, at least to me, to be so routine. Also, her thesis was not published. What advice should I give her? Do I have a responsibility to "turn her in"?
First, the use of the earlier material may have been plagiarism or not. If the methodology was "common knowledge" then it need not be cited.
Second, if sections were copied, verbatim, without citation, then it is still an error but one of copyright violation, not plagiarism. Copyright is about words (actually "creative expression"). Plagiarism is about ideas. Not the same thing. But both need to be avoided.
But, you don't really need to take any action unless you are somehow responsible for academic integrity at the institution. Even then, it may be too late to impose any penalty. Vigilanteism isn't called for. The responsibility for evaluating the thesis was with the university at the time and while they may have failed, it isn't your responsibility to raise a now-dead issue.
If you need to give her advice, talk about the dangers to her career from repeating such things in the future. But I think you can, with a clear conscience, let the past be the past. And be sure that you understand and communicate the difference between plagiarism (mis attribution of ideas, even if paraphrased) and copyright infringement.