Emily Dickinson wept—
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.
I interpret her marks—
as breathless pauses—
that— having no unicode—
should be given to m—
and space—
This list of authors punctuation quirks is interesting though.
https://lithub.com/the-punctuation-marks-loved-and-hated-by-...