I agree that trying to talk it through is a first step, accompanied with insistence on monitoring until it is established that self-care is working, however I also think you need to be prepared take control of the situation now with every means of enforcement that you have available until self-care is back on track. Just as if a 14 year old was hurting themself in some other way - drinking, drugs, unsafe driving, and although D is not their choosing, and we can completely empathize with that, if we let anything get in the way of blood sugar control the consequences down the road could be a lot worse than the (possible temporary) consequences of parental intervention now. My wife and I manage dd's BG overnight as believe at the age of 14 her sleep is more important that ours, and it is enough to ask for her to self-manage responsibly every day. I also think it makes it easier to take a hard line on daytime control if they know that you are equally invested in their care overnight. Part of taking a hard line is having faith that it will be appreciated down the road, even if not always at the moment.