(No deference, I beg you! My interpretations are as debatable as the next person's.)

Here are a few thoughts around Elinor's explanation in chapter 37.

Maybe she just thought she might as well mention everything that had been thrown at her, not just the things that had hurt.

Maybe those two long speeches go back to S&S's epistolary origins. They come across as quite scripted, and quite a mouthful. Emma Thompson made the "After all that is bewitching" line sound natural in S&S2, but IMO normal people aren't articulate enough to pull it off. If I tried to say it aloud and off the cuff, I'd probably end up hesitating and stumbling, more like Colonel Brandon in his 'confession'! And... coming back to the point... maybe in an earlier version Elinor didn't shrug off Mrs Ferrars' nastiness, and JA overlooked** that detail when updating.