Sentence:  Next door, with a roaring fire nine months of the year, is the housekeeper's sitting room, where you may find Mrs Grouse either <WSD>armchaired</WSD> and sewing or desked with a puzzlery of papers, trying, as she says, to 'make head nor tail' of things and — what seems to me contradictory — to make their ends meet. 
Meaning of the word marked with <WSD> tags:  Seated in an armchair.