Duality and identity
The imagery of Nell's self is always mitigated in the most confounding ways by her sister who serves as her foil. Nell is averse to attention, having been over-exposed to attention since her birth on account of her bright red hair. Dolly grew up jealous about that attention and curated skills that help her to navigate polite society better than her sister, not realizing that there was never a reason for competition. The consequence is that Nell grows up feeling like an outcast and a reject, feeling that her prettier sister gets everything she wants.
Marriage as a need
The concrete imagery of courting and marriage comes across much differently to these disenfranchised women. Nell and Dolly understand that they are playing with fewer chips than other women in the community (literally), and therefore, they must attract mates strategically, lest they end up without a spouse during this time in human history when that could have devastating effects on their longevity. The imagery points to a feminist issue; without marriage, how will these girls survive?
The longing of romance
Nell's self-esteem issues keep her locked inside an experience of romance that makes true love like a legendary holy grail. She struggles to keep her heart and mind hopeful because she feels that love might never happen. She falls for this man named Dick, but in a cruel and hateful conspiracy, her sister betrays her and writes to Dick as Nell and tells him never to write back again. This symbolism belongs to the imagery of longing and forbidden love, because Nell is existentially refused love for the reason she feels emotionally plagued about her self-esteem—her cute, conniving, and overly competitive sister.
Religion and God
Nell's life and Dolly's life are both plagued by fates that are sincerely frustrating and confusing. Nell ends up falling in love with someone that loved her back, but then because of petty family politics, Dolly ruined it. Dolly might have been jealous because her own plan to marry a rich man ended just short of the finish line; he dies just before their wedding. Their new marriages are basically the worst kind they could have asked for; they are like family slaves. Nell's journey ends with her confused about the abstract quality of fate; she suspects (probably because of her low self-esteem) that she is secretly being judged by a God who does not like her.
