Sandra may well have a very good memory but I don't think she'd mind me suggesting that her remembering of this particular sermon isn't actually so extraordinary. Several important aspects of the way collective memory works are illustrated by our lunchtime conversation:
Second, Sandra heard the sermon at an event she attended with her mother, and remembers exactly how old she was at the time. The memory is therefore located in another way as well - it carries with it associations of a particular and significant time of life and the sense of belonging to a special social environment that went with it.
Third, the memory carries with it a very strong recollection of feelings. The deep emotions raised were clear in the way Sandra told of the incident and how touched by it those who listened were. This provides yet another kind of location in the sense that the personal significance of the memory remains lively and pertinent.
Fourth, Alyward as the speaker that day spoke with a sincerity of intention that was tangible. Sandra says that afterwards there was so much she wanted to say to Alyward but she was so overcome by the tenor of the occasion and the impact of the speaker that she found herself tongue-tied. Sandra felt that Alyward sensed that and she responded to the youngster by giving her a warm hug. That physical contact adds weight to the memorability of the sermon.
As it happens a recording of Alyward's sermon has recently been found (access it here). The venue and exact date of the recording isn't clear, but its style and content is almost certainly something Alyward repeatedly used during her speaking tours. She speaks straightforwardly and biographically without many rhetorical flourishes, but returns repeatedly to Malachi 3.10. Her conviction is compellingly but undramatically communicated at every point. Interestingly Alyward does not herself described her address as a sermon.
I think every preacher has things to learn from Sandra's remembering. Do we make memory location easy for our hearers? Are we sensitive enough to their current life experiences? Are we connecting to feelings and making what we say emotionally memorable? Are we deliberate enough when it comes to communicating conviction? I suspect if we paid more attention to these things Sandra's remembering wouldn't seem quite so remarkable.