The cafe setting
To set this as a coffee date shows that these girls might not be sisters who connect easily. It suggests a pleasant, public exchange, against which the full personalities of the characters seem almost cartoonish. That's because, as any person with siblings knows, sisters can poke each other's buttons. It seems Monica has an over-bearing relationship to her environment, because she is quite terse with the waitstaff.
Museum imagery
There is polite metropolitan imagery associated with the women's conversation. Specifically they mention the Norman Rockwell Museum, invoking his art, which is nostalgic and pleasant and yet strangely cynical. The museum imagery shows through allusion other cafes (since, arguably, Rockwell's most famous paintings are of cafes), encouraging the reader to take this play as art, and therefore to interpret it, like a painting on a museum wall.
Sexual imagery
Almost randomly, we learn from Claire a dirty secret: neither woman has ever masturbated, except Claire has been...experimenting lately, since she was at a rally and heard about masturbation. The imagery is strong and obvious, and the idea of orgasm is coupled in the play with shame and embarrassment. Although Claire is thrilled, it is clear that the sisters are repressed in general. This is designed to encourage the reader to imagine why they might not feel welcomed to enjoy their own bodies.
Imagery of dominance and submission
Monica's character is shaped by the desire to control her surroundings, including the people around her. We see two modes of domination: major and minor. The major domination is the way she treats her sister, Claire. The implication is that as children, perhaps this was their dynamic. Then, in Monica's treatment of the waitstaff, we learn that she has the same dynamic with strangers, but watered down and more saccharine. Claire shows the antithesis behavior, quietly tolerating her sister with an inner confidence, perhaps gained through private, indulgent ecstasy.
