I've always been kind of curious about this. Are we supposed to believe that it's just all that fresh sea air and exercise? Is it the huge relief of escaping from that claustrophobic Uppercross/Kellynch circle, seeing a new place and meeting some new people? Is it Captain Benwick's conversation, which perhaps gives her the encouraging feeling that there could be new romantic possibilities for her, even if the best she can hope for from FW is friendship? Or (as I'd like to think) is it because she is beginning to sense a revival of FW's interest in her, even before Louisa's fall and "none so capable as Anne"?