I don't think FW's returning interest is a result of Anne's regained bloom: I think it's (arguably) the other way around. One of the things I love about Persuasion is the unspoken dialogue between Anne and FW that is going on under the surface all the time; it's what makes their relationship, for me, one of only two in JA's novels that have a true erotic charge (the other being Darcy and Elizabeth, but never mind). Anne can read him like a book, and she knows that his feelings towards her are changing even before he quite knows it himself. And that realization makes her happier, and therefore prettier.