] It is further evidence of the effect Willoughby has on her. She felt nothing but compassion for the Colonel's "advanced age" and his "forlorn condition as a bachelor"; but no malice. Her more biting remarks were made after she met Willoughby. I think this is one of Jane's early hints that Willoughby is not all he seems.

I'd agree. Frankly, anyone who could abuse the unfortunate Brandon when he's so obviously in distress either lacks perception or compassion, and as Willoughby has enough of the former, he must lack the latter. And it's not the first time that Willoughby has dedicated his wit to maliciously maligning the poor Colonel--the whole "he's the kind of man everyone speaks well of but no one talks to" spiel in Ch. 10. Dashing young men never do turn out to be quite right in JA's novels, do they?