It sounds like you have absolutely no nuance on this subject at all.

In a perfect world teenagers should be more responsible than this yes. In this perfect world those teenagers have a perfect home life, no mental illness or any other form of disability, and are basically not susceptible to being exploited.

Unfortunately things in real life are not that black and white. No 15 year old has these thoughts in a vacuum, they are a result of a combination of factors.

Even if she did all of these things without any external factors at play, she wasnt even given a TRIAL before citezanship was revoked. Even the worst criminals receive trials. She should have been tried in a british court and gone to a British prison for what she has done.