Despite their sibling rivalries, the sisters enjoy each other's company. But they are also cruel to one another. Katja teases Stella about having a moustache (she does not), which results in her trying to shave the imaginary hair with disastrous consequences. Stella tries to emulate her sister's success and takes regular skating lessons at the same rink. Although it is Katja who has the eating disorder, the story is told from the perspective of Stella who after witnessing her sister vomiting up her food wants to tell their parents.
Katja forces Stella to remain silent by threatening to reveal her infatuation with Jacob. Lenken focuses on Stella's dilemma - her fear that her sister will die is set against the unbearable thought that her crush on Jacob will be revealed. In a childish act of revenge Stella get a friend to make an anonymous call to Katja telling her that she smells of vomit and will die if she doesn't eat. Gradually, increasingly preoccupied with her sister, Stella's school work starts to suffer and she reaches breaking point. Josephson steals the film. Frequent close-ups of her face convey her anguish, frustration and jealousy in vivid detail. She is also struggling to forge her own identity and in fact has more friends and interests than Katja who is obsessively dedicated to fitness training.
Bittersweet humour comes in the form of Stella's meetings with Jacob where she attempts to charm her way into his affections. Deasismont is also very good as an adolescent high achiever, at the mercy of her hormones, subject to frequent and irrational mood swings and incessantly crying. Inspired by her own teenage battle with anorexia, Lenken explores the intersection of body image and self-esteem with sensitivity and compassion. Copper-haired Josephson is particularly mesmerising. Beautifully and unobtrusively shot by Moritz Schultheiß, My Skinny Sister is a tender portrait of teenage angst and a salutary warning against the dangers of obsessive calorie counting.