Unfortunately my fair use is her plagiarism is your copyright violation. Fair use was intentionally never very clear, but recently, IP rights owners have forced changes to laws, different in every jurisdiction, that have forced fair use to the margins.
What you describe is certainly not plagiarism as the words being used are correctly attributed to their creators. Dangerous ground if you use quotes without attribution, however. You shouldn't give the impression that words are yours when they are not.
But is it fair use?
Traditionally, I'm pretty sure that almost everyone would say yes. Fair to use the actual words in this way provided that they form an insignificant fraction of the whole work being quoted and proper attribution is given.
But now it is not so clear.
If you are at a University or other large institution, you likely have lawyers available that can give advice on this that is particular to your own situation (country, etc). There may also be a Research Office that has looked into this question and can provide guidance.
It might even be that paraphrasing is considered more troublesome than direct quoting.
But copyright is currently a moras. We are moving in many places toward unlimited and absolute copyright. Academics, especially, should work in the political realm to halt this trend before it makes some research fields impossible.