Ha, good point, and an interesting question: What kinds of dashes did Dickinson intend?
It's a hard one to answer: We could look at published Emily Dickinson books from the time, but did Dickinson really pay that close attention to or have that much control over the type?
We could look at Dickinson's actual personal documents, but if they were handewritten, distinguishing dashes could be difficult even if there was intention there.