I have had this person edit countless documents for me over the last three years, everything from letters of recommendations for others (where she catches additional things to be included), to important correspondence where a single typo can create a poor impression. She is a great editor who can not only catch the form/from, does/dose kind of typo that gets by spell check, but she makes recommendations for improving flow and writing in a more active tone.
I know she has worked with many researchers and amassed over 30 full scientific journal articles. Some people she worked with were not native English speakers and she also served as the editor of their work making sure it was grammatically correct and understandable to an English audience.
In addition to being a great editor she is also a good writer. After I created a department newsletter, I sent her out to interview a faculty member for each edition. She has a natural talent for not only getting the mundane details of their work but also getting to the more personal side of them. The faculty universally loved her interviews in our newsletter.
I give her my highest recommendation.