It occurred to me that perhaps Capt. Wentworth confuses a strong mind with being headstrong. Louisa Musgrove is headstrong, which leads her to hurt her head. Luckily, she has a strong head and recovers. Anne has developed a strong mind, ie sure of her opinions, but is so quiet and unassuming that he doesn't see it right away.
Funny, the first time I read this novel, I didn't think much of it. I had even forgotten that I'd read it! But now, I love it!