Sara Louise, the main character in the book, is alienated, but capable and resilient.
Sara Louise has always lived in the shadow of her twin sister Caroline. More obviously needy because of her fragile health, Caroline has received the lion's share of attention from her parents, and her golden looks and personality cause others to immediately take to her at the expense of the more dour Sara Louise. Feeling rejected and unloved, Sara Louise becomes bitter and hateful, further contributing to her alienation.
There is no doubt that Sara Louise is capable in many ways, but to her this is more a curse than a blessing. It is she who contributes to the family income with crabbing skill, but convention frowns upon girls working with the men on more challenging endeavors like oystering. More to the point, it is Sara Louise's ability to get things done that brings her family to depend on her while they pamper her more frail sister. Sara Louise feels that because she is able to get by on her own, she is taken for granted.
Though many of her problems are arguably brought about by herself, Sara Louise really does bear disappointment after disappointment with resilience and strength. It is hard for her to see her sister get so many of the things she herself wants - attention, boarding school, and McCall Purnell. Yet Sara Louise endures, finally coming to the realization that only she can change the circumstances of her life.