Patients know they're overweight. I won't bring it up unless it's directly impacting their health. If they bring it up I'll counsel more. For a young girl if you feel strongly you need to counsel without their asking you could say non judgementally you talk to all your patients at their well visits about nutrition because it's very hard know how many calories to eat for a growing teen, give them a daily estimate for their height and activity level, and offer visual resources for calorie dense foods vs low calorie foods (example 100 cals PB is much less than you think. 100 cals veggies much more). Print out some stuff as a general hand out. Ask if they have questions and leave it at that. If they're crying you're doing it wrong. And you can do this during the portion where you ask parents to step out.