I think it's justifiable to call out her contribution. She was an excellent editor without Star Wars, her work includes American Graffiti and Taxi Driver. I consider her a part of what makes the original trilogy great but I don't think it diminishes Lucas' contribution.
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 .