Like Clare from All That Glisters and Mary from Hieroglyphics, Alison suffers from a deep sense of isolation. This isolation is shown to be a result of her familial relationships.
mammy disnae love me
Her jealousy creates an emotional barrier between herself and her sister, and her mother. Her father is only a minor figure in the story, perhaps mirroring his impact on Alison's life.
Alison overhears grown-ups commenting on her size and this furthers her sense of isolation. She lacks confidence, which means she is not able to express her feelings to anyone, even Santa.