I suppose, the realism of story represents the main virtue of this coming of age short film. The 12 years birthday of a girl. The tradition of pinata, sustain by entire family. The influence of her friends, sophisticated girls who, from make up and fancy dress . And , not the last, the boy who represents her secret chosen.
The party reflects the fight between tradition of family, perceiving her as child and the influence of two friends , young people more than parts of near reality.
So, the reactions of Mia are ambiguous and her younger sister is the best observer in this sense.
The result, a beautiful well crafted short film.