The fourth letter perhaps gives us a picture of Cassandra. There was a post here where one wondered if she was too serious and stern.

Cassandra's humour must have been so like Jane's, that she 'could die of laughter'.
There is nothing in letter 4 that could be a comment of what was written in Cassandra's letter.

Does anyone know anything about the letters from Cassandra?
What did Jane do with them?
What must Cassandra have written?
So many questions.