How is the theme of rebellion presented in "For Heidi with the Blue Hair"?

For Heidi With Blue Hair by Fleur Adcock is a poem centered around the theme of rebellion and the expression of individuality.
The main character in this poem is a young student, Heidi, who dyes her hair blue as an act of personal expression and for this is sent home from school. Although Heidi is portrayed as strong-minded and rebellious, dyeing her hair is probably more a question of affirming her identity. In fact, she checks the school rules and asks for her father's permission before dyeing her hair; while she may sense that blue hair may be perceived as rebellious, the "law" is on her side. There is nothing in the rule book that prohibits dyed hair, but the school sends her home anyway with the weak argument that blue is not one of the school colors.
Heidi is distraught at being sent home; she is in tears, and this allows us to see a softer, less rebellious side to her. Her father supports her and calls the school to say that she is not a punk or a rebellious girl, but her choice in hair color is, in fact, just a style. Her hair color is permanent, so she can't wash it out. Heidi is now determined to keep her new hair color. 
It is at this point that we learn that Heidi is going through some serious personal issues; her mother has died, though the father does not wish to mention this to the school. The school, in any case, does not argue any further and lets the issue slide. The following day, her classmate comes to school with her hair dyed in school colors: grey, white, and yellow. This is a clear act of solidarity with Heidi and an act of rebellion against the school.
As the poem is addressed directly to Heidi in a colloquial way, we end up sympathizing with her and seeing the school as a questionable authority, especially since the arguments it presents are particularly flimsy. The real issue for the school is the need for conformity, a difficult issue when dealing with teenage students. However, we also realize that teenage rebellion may have deeply rooted causes that are not immediately apparent to others. 
The loose structure, the use of simple, conversational vocabulary, and the absence of a rhyme scheme help reinforce the idea of rebellion. The battle against authority and rules is therefore depicted in the poem's structure as well as its content.