Being a photographer, I wasn't my duty to give Sumire these photos personally. But she still didn't know her co-workers well. Or/Nor the other way around.
Should it be "or" or "nor"? Why?
You should use nor since it is a negation, but your sentence
But she still didn't know her co-workers well. Or/Nor the other way around.
can the transformed to
But she still didn't know her co-workers well. Nor did they know her.
and could be expressed more clearly as
But she and her coworkers didn't know each other well.