I agree the rumor there is an attraction between Jane and Mr. Dixon or even worse that Jane seduced his affections away from her friend, Miss Campbell or his wife, Mrs. Dixon would be ruinous to her reputation. I am so glad it is confined to Emma’s imagination. I think at this point Emma is romanticizing Jane into a martyr:

When she took in her history, indeed, her situation, as well as her beauty; when she considered what all this elegance was destined to, what she was going to sink from, how she was going to live, it seemed impossible to feel any thing but compassion and respect; especially, if to every well-known particular entitling her to interest, were added the highly probable circumstance of an attachment to Mr. Dixon, which she had so naturally started to herself. In that case, nothing could be more pitiable or more honourable than the sacrifices she had resolved on. Emma was very willing now to acquit her of having seduced Mr. Dixon's affections from his wife, or of any thing mischievous which her imagination had suggested at first. If it were love, it might be simple, single, successless love on her side alone. She might have been unconsciously sucking in the sad poison, while a sharer of his conversation with her friend; and from the best, the purest of motives, might now be denying herself this visit to Ireland, and resolving to divide herself effectually from him and his connections by soon beginning her career of laborious duty. (20)