Mike, the question of whether or not a 16 year old can legally play the lottery in the UK is to a certain degree a question of literary license. I am also a writer, with two books published so far, and on one of the ones I am working on I had a question about a real estate easement that was far more complicated than your question. I was advised, by a lawyer on these boards (though he does not post on this forum), that I should do what was right for the story and leave the question of strict legalities alone. My concept was one that could play out many different ways - I should simply pick the one that worked best for me. If you were told by the UK National Lottery that your character could play the lottery as long as she was physically present in the UK at the time, that should be good enough. Go ahead with your story the way it works.