Here Marianne has been weeping and moping for weeks over a temporary separation from Willoughby (for which we have no patience, yes?), and Elinor - who has every reason to be truly unhappy at this point - puts on something approaching a happy face, choosing to follow the advice of the dance instructor in the movie Object of My Affection: "Chin up, young person."
Here's where we start to see something like a balance of sense and sensibility (remembering that the second word means "feeling"). Elinor takes her leave from the odious Lucy Steele and goes home to cry it out - alone. She doesn't FORCE herself to cry, the way Marianne did; rather, she allows herself to feel her sorrow, then takes some time to think things through.
She quickly determines that Lucy and Edward truly are engaged, and at first, she's angry with Edward for having led her on. She's not able to sustain that anger all that long, however, since she starts to look at things more reasonably: Edward, now 23, got engaged to Lucy when he was only 19 (and she was probably about 17 or so). Elinor reasons her way through what must have happened, and is able to explain to herself (and to us readers) precisely what must have happened - Edward committed himself to Lucy too early, then outgrew Lucy, then fell in love with Elinor. Elinor realizes that his hot/cold behavior was him trying NOT to lead her on, and she forgives him easily for his behavior - and so tender are her feelings, that she cries again: not for herself, but for poor Edward, who is in for a lifetime of disappointment.
Truly, Elinor has a big heart, and a great burden of grief. The only people who know it, however, are Elinor and us - the readers, who are privy to her secret and to her pain. Elinor also has massive balls - or whatever the feminine equivalent are - for this:
Much as she had suffered from her first conversation with Lucy on the subject, she soon felt an earnest wish of renewing it; and this for more reasons than one. She wanted to hear many particulars of their engagement repeated again, she wanted more clearly to understand what Lucy really felt for Edward, whether there were any sincerity in her declaration of tender regard for him, and she particularly wanted to convince Lucy, by her readiness to enter on the matter again, and her calmness in conversing on it, that she was no otherwise interested in it than as a friend, which she very much feared her involuntary agitation, in their morning discourse, must have left at least doubtful. That Lucy was disposed to be jealous of her appeared very probable: it was plain that Edward had always spoken highly in her praise, not merely from Lucy's assertion, but from her venturing to trust her on so short a personal acquaintance, with a secret so confessedly and evidently important. And even Sir John's joking intelligence must have had some weight. But indeed, while Elinor remained so well assured within herself of being really beloved by Edward, it required no other consideration of probabilities to make it natural that Lucy should be jealous; and that she was so, her very confidence was a proof. What other reason for the disclosure of the affair could there be, but that Elinor might be informed by it of Lucy's superior claims on Edward, and be taught to avoid him in future? She had little difficulty in understanding thus much of her rival's intentions, and while she was firmly resolved to act by her as every principle of honour and honesty directed, to combat her own affection for Edward and to see him as little as possible; she could not deny herself the comfort of endeavouring to convince Lucy that her heart was unwounded. And as she could now have nothing more painful to hear on the subject than had already been told, she did not mistrust her own ability of going through a repetition of particulars with composure.That's right - Elinor wants to find out whether or not Lucy is actually in love with Edward, and she also wants to be sure to things over so that Lucy won't be sure she's gotten to Elinor. It's for that reason that she accepts an invitation to an assuredly tedious dinner party with Lady Middleton, who passive-aggressively gets Lucy to work on a gift for that three year-old that was crying a few chapters back.
We are again invited by Austen to compare the Dashwood sisters: Both have something they'd like to do far more than playing cards with Lady Middleton. Marianne declares that she hates cards and will play the piano instead, thereby offending her hostess. Elinor (who wants a chance to chat with Lucy) offers to help Lucy with the filigree basket, allegedly out of a desire to please Lady Middleton's child. She manages to be excused from cards AND earn Lady M's approval, a point Austen can't help but belabor.