I certainly did not owe the suggestion of one incident
A long critical history has sprung up around this statement. Now that all the extant manuscripts for the novel have been published in facsimile, it would appear, at least from the written evidence, that Mary Shelley's defence of her own artistry is accurate. Her husband read the manuscript with careful attention, here and there suggesting variations in phrasing that Mary Shelley incorporated into the final form of the novel. As the editor of the facsimile edition concludes, "A reading of the evidence in these Frankenstein Notebooks should make clear that PBS's contributions to Frankenstein were no more than what most publishers' editors have provided new (or old) authors or, in fact, what colleagues have provided to each other after reading each other's works in progress." For the full statement, see Charles E. Robinson, ed. The Frankenstein Notebooks: A Facsimile Edition (New York and London: Garland Publishing, 1996), I, lxvii-lxx.