One reason why Isabelle- Marie hates Louise is because of how her mother loves superficially. Louise is in love with anything that is beautiful. Her love for Patrice is reflective of this. Beauty and superficiality is what motivates Louise's love. In contrast to this, Isabelle- Marie is not beautiful. The lesion that grows on her face, denying her physical sense of beauty is reflective of her attitude towards a world in which the superficial is praised and prized above all else.
Isabelle- Marie hates her mother because she is a reflection of the world. She is crushed by her mother's lack of attention and emotional abandonment because it is a stunning reminder as to how cruel the world is. In this context, motherhood is not the shelter from the storm. Rather, it is the storm in that it reaffirms it. Isabelle- Marie feels this and the growing lesion on her face is reflective of the growing hate and anger that is within her. This is motivated from her mother's lack of love and affection towards her. It is also driven by the fact that the mother, Louise, is an extension of the world's cruelty and not a repudiation of it.