The Taming of Marianne is harsh but not unfair. She just wants a beautiful love story! And unfortunately the guy who shows up is Willoughby. (Rereading the scene where Marianne is sharing all her favorite poems/songs/etc, the brutal thought occurred to me that he's probably just PRETENDING to love all the same art. "Don't you think Cowper is so beautifully melancholy?" Marianne probably says, and all Willoughby has to do is nod fervently and say "Oh indeed.")

I get why Lucy mentions her secret engagement to Elinor the first time, but the way she just keeps rubbing it in! So mean. But probably Lucy doesn't understand that Elinor will stop pursuing Edward once she knows that he's engaged: if their positions were exchanged Lucy certainly wouldn't give up. So she has to go on and on about it to neutralize what she sees as the threat of Elinor's interference.