I expected to have heard from you this morning, but no letter is come. I shall not take the trouble of announcing to you any more of Mary's children, if, instead of thanking me for the intelligence, you always sit down and write to James. I am sure nobody can desire your letters so much as I do, and I don't think anybody deserves them so well.Having now relieved my heart of a great deal of malevolence.....

It may be couched in humour but I think underlying it all is a little irritation.

Poor JA- in charge of the household,not her normal role in the family, and the staff are at sixes and sevens;Mrs Austen still ill with suspected liver problems:

He [Lydford-JW]wants my mother to look yellow and to throw out a rash, but she will do neither.Letter 13

It was also November- short days,and possibly inclement weather.

I can quite understand why she needed the comfort of Casandra's letters.