If my supervisor sugests a very specific addition to something, can I use it verbatim? Say you send a document, it could be a report, or a literature review, or a draft paper, to your supervisor. They write back something along the lines of;


  Yes, looks good. You need to define the foobar and also add somthing
  to section 3 like; 
  
  The demonstrates the fungability of baz in the context of high energy
  ice cream sundays. The delicious factor is an extreme motivator.
  
  Yours
  - Dr Sprinkles


They are clearly not asking for it to be put in as a quote, but is it expected that you would use some or all of it verbatim? That feels odd since it was written by someone else, but rewording it just for the sake of rewording it could result in something distinctly awkward. 

Does the nature of the document make a difference?
In my experience with suggestions like these, the idea is that you more-or-less insert it verbatim, with edits for style (after all, your supervisor probably wrote it off-the-cuff) and flow with the surrounding paragraphs.

Your supervisor is probably a better writer than you, and so her suggestion is most likely a good one. If you really hate it, you aren't obliged to use the phrasing (but using the ideas is probably good).

If you're feeling "odd" about using someone else's writing, I wouldn't worry. Either she is already a co-author on the paper, or she's helping you edit with no expectation of receiving credit for her short suggestion. If you're still worrying, make sure to thank her in the acknowledgements or something.

It seems remarkably unlikely that there is any plagiarism concerns here. For one, this looks like a concluding sentence, so it's unlikely she's plagiarizing a write-up of results she is only just helping to write up. Secondly, as I mentioned, suggestions like this are usually made off-the-cuff. If you are very concerned, Google the phrasing and make sure she's not subconsciously copying it from a paper she didn't author.