In These Happy Golden Years, Nellie manages to weasel her way into joining Laura and Almanzo on their Sunday buggy rides, Almanzo being completely clueless as to her actual motives (she's out to drive Laura away, either because she's sweet on him herself or just to piss Laura off, or both). Laura, unwilling to cave, lets the edge of the dust-robe (basically a blanket designed to keep dust off the riders' clothes) flap like a sail and scares the horses into bolting. Nellie freaks out along with them, throws a fit, and declares she'll never ride behind those maniac horses again. When Laura and Almanzo later take her friend Ida for a drive, Ida is surprised anyone could be afraid of such gentle horses, at which Almanzo looks at Laura, who just smiles and tucks in the dust-robe a little more securely.
Not just that, but shortly after the incident in which the horses bolt, during the same drive, Laura suggests following the road they're on a little farther - because she knows that the first opportunity that they'll have to turn back towards town will take them past the Olesons' claim first. What makes this really amusing is that she makes the suggestion while they've stopped for a brief visit at the claim of some family friends, and Mr. Boast, clearly catching on to Laura's intentions, helps out by cheerfully assuring that "it's a good road straight north." Nellie is very unamused.
At the point where Mary is attending a school for the blind, during a visit home she relates a story of a shopping trip she took with a friend who, while legally blind, can make out colors. Her friend picked out handkerchiefs by color and lead the storekeeper to believe that she could tell color by touch.
It becomes a Crowning Moment of Heartwarming when Laura decides everything she's gone through teaching school is worth it, because when Mary tells the story, it's the first time she's actually laughed since before she went blind.