Meaning of sentence ending もん > **** > > "You occasionally hear stories of being chased by stray dogs even in my class" said her sister calmly, following on from dad. My understanding of comes from this answer, which suggests that the ending makes the sentence somewhat emphatic. But this doesn't seem consistent with the sister speaking calmly (). Does have another meaning? What am I misunderstanding?

It's within the "emphatic" use of in my opinion. might be better translated as "coolly" in this case. suggests the person in focus ( in this case) is being/looking cool-headed while someone else is overly excited. In other words, I would imagine she is not too loud but sounds confident.