“Oh! never, never, never! he never will succeed with me.” And she spoke with a warmth which quite astonished Edmund, and which she blushed at the recollection of herself, when she saw his look, and heard him reply, “Never! Fanny!— so very determined and positive! This is not like yourself, your rational self.”

I think she is acting like an emotional, drama-queen teenager here, which isn't like her normal, rational self. Just my take on it. Maybe I'm seeing my 17 year old daughter way too much during this read. While my daughter is by no means comparable to Fanny, that emotional roller coaster of the world ending one minute and everything is beautiful the next really hits home with me right now. :-|