It's been mentioned, but I should emphasise that 'our Jane' (or dialect forms such as 'wor') is felt very much as a Northern form. It's one of the instantly available features you can use to place or caricature someone, especially the vocative use. So someone consciously dropping her roots, using Southern 'but' vowels instead of the 'put' sound, wouldn't use it.
If the TV adaptation of 'Pride and Prejudice' used 'our mother' then it modernised it to avoid a jarring effect. Jane Austen's characters always say 'my mother', even between sisters:
In reply to:
Elizabeth jumped out; and, after giving each of them an hasty kiss, hurried into the vestibule, where Jane, who came running down stairs from her mother's apartment, immediately met her.
Elizabeth, as she affectionately embraced her, whilst tears filled the eyes of both, lost not a moment in asking whether any thing had been heard of the fugitives.
'Not yet,' replied Jane. 'But now that my dear uncle is come, I hope every thing will be well.'
'Is my father in town?'
'Yes, he went on Tuesday, as I wrote you word.'
'And have you heard from him often?'
'We have heard only once. He wrote me a few lines on Wednesday, to say that he had arrived in safety, and to give me his directions, which I particularly begged him to do. He merely added that he should not write again till he had something of importance to mention.'
'And my mother -- How is she? How are you all?'
'My mother is tolerably well, I trust; though her spirits are greatly shaken. She is up stairs, and will have great satisfaction in seeing you all. She does not yet leave her dressing-room. Mary and Kitty, thank Heaven! are quite well.'
So Elizabeth and Jane say 'my mother' to each other in direct sequence, as well as 'my father', 'my uncle', and the author uses 'her mother' not 'their mother'. I did a search, and the expression 'our mother' doesn't occur at all in the book.
