A Preface to Paradise Lost: Miss Bates

Lewis opens his chapter on Satan:

Before considering the character of Milton's Satan it may be desirable to remove an ambiguity by noticing that Jane Austen's Miss Bates could be described as either a very entertaining or a very tedious person.

Lewis isn't comparing Miss Bates to Satan. Rather he is preparing the reader to understand why some literary criticism could make "the proposition that Milton's Satan is a magnificent character" in one of two senses.

(1)"It may mean that Milton's presentation of him is a magnificent poetical achievement which engages the attention and excites the admiration of the reader"

(2)"On the other hand, it may mean that the real being (if any) whom Milton is depicting...is or ought to be an object of admiration and sympathy, conscious or unconscious, on the part of the poet or his readers or both" (p 94)

So either the author's portrait entertains us while we reador if we met a person like Miss Bates in real life we (like the other characters in Jane Austen's Emma) would find Miss Bates tedious.

So that's the extent of the similarities between Miss Bates & Satan: purely a comparison of effect upon the readers of their respective portraits by Austen & Milton.