I love the way in which you have taken one quotation from the play and fully picked it apart and analysed each part in much detail. However, I think there is some scope for improvement. You could say that the use of the word 'labour' instead of 'work' or another job-related lexis is used in particular as it has connotations of heavy work, and the employers working the girls to the bone, and how there is an imbalance in the profession with the use of the word 'cheap' because normally, labourers are paid reasonable sums of money, as cheap here is ambiguous. It could mean the actual wage that the girls are paid, if anything, but also insinuates the way in which the girls in the factory are exploited, which you could link back to the sexist nature of the working class and the aristocracy. Sheila comes across as disgusted and outraged, but also shocked - this is a milestone in the play because Sheila had no care for those lower than her, a feature of her personality which was heavily influenced by her parents in particular, and perhaps also Gerald. The hyphen shows that she is coming to realise the real flaws in society at the time, ie. she no longer sees the world through rose-tinted spectacles, but through harsh reality, because on one side of the hyphen is part of the view that she must have had prior to the Inspector's ominous arrival, and the other side of the hyphen is a personal realisation that she finally understands the word 'people', thus also humanising the girls in the process.
I believe I might have touched on some of your excellent points, and repeated them in the process but I do hope that some of my further analysis has helped you as much as possible. For an essay itself, I believe you wou;ld need at least one or two more quotes, but no more, whatever the question. In addition, I think you need to link each quotation back to the purpose that J.B.Priestley intended his phenomenal play to serve. I would give your paragraph a high Band 5 (I believe this is the second to highest band), because I think you need more analysis in there (just write everything down that comes into your head, and then expand on those points) and linking back to Priestley's purpose(s) and of course the question, or statement, whichever.
I hope this helps and I am sorry if I come across a bit harsh in marking - I am simply conveying to you what my English teacher said to me to do in such an essay, because those tips really helped me to get an A* in English Lit
. If you need anything else, don't hesitate to ask me, and good luck in the exams!