on her heart's feelings as she usually does, coming up with this about Captain Benwick:

"And yet," said Anne to herself, as they now moved forward to meet the party, "he has not, perhaps, a more sorrowing heart than I have. I cannot believe his prospects so blighted for ever. He is younger than I am; younger in feeling, if not in fact; younger as a man. ***He will rally again, and be happy with another***."

IMO, Anne never really entertains the idea of Captain Benwick because her heart is already spoken for, privately, as far as she sees it. She is very sorry for him, helps him, and feels a kinship, but not an attraction. In this way, if she had stayed, I think it would've been a disappointment to Captain Benwick in the long run, because her heart was already entwined with it's own longings and wishes, private to everyone but the reader.

By what she says above, she is already setting him apart, as she has accepted her enforced spinster role, and sort of separates him from herself, perhaps because of this. He is younger than her, and has more resilience. In this way, Louisa was right for him, because she was injured, and he played a part in "saving" her, possibly assuaging some guilt maybe, and probably helped and eased the pain over Fanny's death. By helping to heal another, he is able to heal also, in many ways.

I don't really think there was any danger in Captain Benwick having Anne, as he didn't come to see her either, later on, and Anne would have sensed this was because the attraction to her wasn't strong enough. Just my thoughts on what she says. Hope it makes sense.