What is the message behind Hay Carmela ?

Part of an assignment is to write about the hidden message of a spanish film we watched in class called hay carmela but i cant think of one. The story goes that there is a group of three perfomers during the spanish civil war, a man, a woman and a boy who cannot speak. They are republicans and perform for republican soldiers and towns. They are on their way to valencia (another republican place at the time) and meet nationalist soldiers on the way who capture them and hold them in a school. They are scared as sometime they come into the school and kill random prisoners. In order to survive they have to perform for the nationalists a sthey have promised them freedom if they do. However during the performance the woman is upset my some anti-republican comments and starts to shout out to the audience, revealing that she is a republican. A soldier in the audience then shoots her in the head and the boy regains his voice in shock. The film ends whith a scene of the boy and the man placing flowers on her grave. Obviously its a sad story about the spanish civil war but what is the "hidden message" as my teacher asks? i dont really understand, any help appreciated :)