She won the Oscar for editing "A New Hope"
I don't think its mythology to claim that Marcia Lucas edited the films. It's pretty well accepted reality.
If the remasters and the episodes I-III are anything to judge by, George really does better when there is an editor that will check him.
Marcia Lucas along with two other editors won the Film Editing Oscar for Star Wars/ANH/Ep. 4 ( https://www.youtube.com/watch?v=w1dW6bNBzN8&t=52s ): she was no doubt a very good editor. Neither she nor the other two "saved Star Wars in the edit" in the manner often claimed. For example, Marcia Lucas fought to keep the teen-movie version of the opening with Luke meeting Biggs and others at Tosche Station in Tatooine, while George Lucas had always preferred to begin the Tatooine segment with the droids https://www.youtube.com/watch?v=olqVGz6mOVE&t=1407s .