I forgot to discuss Lucy in my previous post. :-)

"Perhaps, Miss Marianne," cried Lucy, eager to take some revenge on her, "you think young men never stand upon engagements, if they have no mind to keep them, little as well as great."

There is a pun on the word engagement. Marianne chides Edward for waiting so long to visit them--even though Edward states that he has had other engagements (obligations).

And, as Mandy points out, it's also a dig at Marianne about Willouhgby. Although Marianne and W. were never formally engaged, the London gossip said that they were. In marrying Miss Grey, Willoughby doesn't keep his "engagement" to Marianne.