Kevin - I couldn't come across any evidence that Dickinson and Beecher ever met either, after rashly naming him (I figured the fact you called him a "Presbyterian" minister was a red herring to put us off the scent, as he was a Congregationalist but of course could, and did, serve as the pastor of Presbyterian churches.)
 
The closest I came just now in a brief frenzy of Googling was the fact that she heard him speak at the 1862 Amherst commencement, noted in Christopher Benfey's "A Summer of Hummingbirds." And of course, as you note, he was a family friend. But that doesn't supply the face-to-face encounter you required. Unless someone else supplies it, I am happy to withdraw from the field and congratulate the two real winners!
 
Cheers,
Steve

Steve Courtney
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