Elinor's reaction when Willoughby coldly breaks up with Marianne via letter and returns all her letters and lock of hair. For all the disagreements they've had and their differences in temperament, the first thing Elinor does when she finds Marianne is to take her hand, kiss her, and just silently hold her while Marianne cries.
Marianne's spirited defense of Elinor's artwork when Mrs. Ferrars sneers at it. Even though it attracts more notice than the sneer itself, it just shows how much she loves Elinor. (And Colonel Brandon's regard is increased all the more to see her refuse to sit idly by while Elinor is abused.)
The way Elinor and Marianne come to appreciate and finally love Mrs. Jennings, who may be annoying, a little ditzy, and never shuts up, but who is utterly and unfailingly kind and loyal to them, whatever they're going through.
Sir John and Mrs. Jennings' complete friendliness and hospitality towards Mrs. Dashwood and her daughters. After how abominably they've been treated by their immediate family it's nice to see someone extending the hand of friendship. And while Sir John and Mrs. Jennings can be a bit much at times, neither of them has a mean-spirited bone in their body.
When Marianne is led out of the ball in evident distress, Mr. Palmer notices and appears rather concerned even though he's caught up in a dance. From then on he goes out of his way to be kind to the Dashwood sisters, offering Elinor any possible assistance when Marianne falls ill.
After her fever has broken, Marianne asks first for Elinor, and then Colonel Brandon.
Toward the end of the movie, when Edward comes calling to the Dashwood ladies. This is after the women had heard that Elinor's rival for Edward's affection - Lucy - had gotten married. During the awkward exchanges, Edward reveals that Lucy had in fact married Edward's younger brother. Elinor's reaction upon hearing that is pure CMoF, but this falls under Heartwarming because of the joyous grin on Elinor's face, and from what Margaret reports spying from her treehouse: