George Eliot on Silly Novels by Lady Novelists, as written in 1856:
The heroine is usually an heiress, probably a peeress in her own right, with perhaps a vicious baronet, an amiable duke, and an irresistible younger son of a marquis as lovers in the foreground, a clergyman and a poet sighing for her in the middle distance, and a crowd of undefined adorers dimly indicated beyond. Her eyes and her wit are both dazzling; her nose and her morals are alike free from any tendency to irregularity; she has a superb contralto and a superb intellect; she is perfectly well-dressed and perfectly religious; she dances like a sylph, and reads the Bible in the original tongues. Or it may be that the heroine is not an heiress — that rank and wealth are the only things in which she is deficient; but she infallibly gets into high society, she has the triumph of refusing many matches and securing the best, and she wears some family jewels or other as a sort of crown of righteousness at the end. Rakish men either bite their lips in impotent confusion at her repartees, or are touched to penitence by her reproofs, which, on appropriate occasions, rise to a lofty strain of rhetoric; indeed, there is a general propensity in her to make speeches, and to rhapsodize at some length when she retires to her bedroom. In her recorded conversations she is amazingly eloquent, and in her unrecorded conversations, amazingly witty. She is under stood to have a depth of insight that looks through and through the shallow theories of philosophers, and her superior instincts are a sort of dial by which men have only to set their clocks and watches, and all will go well.
Found via TV Tropes (don’t click if you want to do anything today), it shows Mary Sue is one of the oldest tricks in the book.