Brenda Hill has some very good reasons why Aunt Helen, who taught English for so many years, isn't the best editor for your manuscript.
When you edit your own work, the easiest way to find things you want to change or correct is to start at the end of the piece and read one paragraph at a time. This tricks you into seeing what's actually on the page instead of what you KNOW you wrote there (missing, wrong, or overused words and phrases, missing punctuation, etc.). Many times you'll find a better way to say something, making for a better story. At the very least, you'll make it easier for your editor to help you.