I think a bit of a carrot and stick approach might work here. Carrot - She will perform better if she is within range, maybe having to take a little time to have a juice if she is going low ( but you might mention to her that it is much quicker to get up from a low than down from a high - another carrot). I would also reassure her that because of the cgms she does not have to be worried about going really low without warning (unless the batteries dislodge in the receiver!!!) (Nav problem). Stick part - not allowed to do so much sport unless she makes a little more effort and keeps in range. My educator did once tell me that teens compliance with diabetes care has to be treated like homework. If you don't do it there are consequences. Find the things they love the most and withhold them for non-compliance. Sport in this case. This is a hard line but would work - and she is old enough to catch on quickly.