] "Could", I believe, is the operative word. Where she previously could NOT, now she COULD and this is her change of sentiment.

If could is the operative word, then I would think that the point is that, which it has become possible for her to fall in love, she hasn't yet.

] By this time it is my opinion that she's already somewhat smitten and conflicted, but then I am one of those crazy people who thinks Elizabeth is attracted to Darcy from the moment of their meeting.

I would think that this passage supports the opposite interpretation, not just of Lizzy's feelings of the moment but of her feelings about Darcy throughout the book. Before, she was not attracted to him, and it would not have been possible for her to love him. She sees that her previous objections have been dealt with, and not only dealt with but (dare she even think it?) perhaps dealt with as a result of her own words. Now it is possible for her to fall in love with him. She hasn't yet, but it has become possible.