Sheila is warning her family about pretending to be detached from or superior to the situation
The use of slowly and carefully in the stage directions imply that Sheila is thinking carefully about how to get this complex issue across
The use of wall is a metaphor for the boundaries that the Birling's are trying to put up between the different classes and between themselves and the situation
The phrase anything but a joke shows that the younger generation understand and are more socially aware than the older generation
The use of the imperative tell show Sheila standing up to her family, challenging them with self confidence and certainty
The adverb hysterically in the stage directions implies that Sheila has an early understanding of the inspector and is getting somewhat frustrated at the fact that the others are still pretending
Sheila insults Gerald with the phrase you fool to signify that he is a fool compared to the knowledge of the inspector
The use of the verb knows builds on our understanding that the inspector is omniscient, meaning that he knows everything
The phrase their people tells us that Sheila does in fact carry some socialist views, believing that the women who work in factories are not just objects but individuals
Sheila is mirroring the attitudes of her family before the inspector arrives and alters them, showing that she is materialistic and only sees true value and truth in her relationship to Gerald once he has given her a piece of jewelry
Sheila's response of now I feel really engaged conveys the capitalist idea that wealth is more important than affection