I know that she takes in the rebellion of V and moves forward with it, but then she dies. Is that a take on the casualties of a rebellion, the fault of oppression, or just showing that children are impressionable? I can't exactly tell.
It represents all that you have cited but most importantly, our relationship with the young girl that develops throughout the film is meant to give us the most amount of context by the time we get to the 'Domino' montage. From all of the consequences following V's attempt to escalate the anarchic situation, it is her brutal and disproportionate murder that seems to provide the final catalyst in galvanising the denizens of the 'Norsefire' regime. The subsequent retaliation against the Fingerman is the most overt demonstration of the population's final rejection of the oppressive regime they are under, showing that it is not only those considered 'deviant' that are at risk from the brutality and that a child is now subject to a summery execution for having nothing more than a progressive thought.