16 yr old has chronic bad breath. Dentists say not teeth/gums. Read about tonsil stones. It looks like she has 1. Should I take her to dr? Any info?

See ENT. By all means see ear/nose/throat specialist. Also see dentist as flossing and/or water pik daily to clean between teeth, where toothbrush can't reach, and/or using tongue scraper, may help.
Yes. She should see a doctor. It may be a digestive problem- h. Pylori is a common stomach infection which can cause bad breath issues. There could also be a sinus infection or other causes. Check with her doctor.
Other causes, too. Halitosis can be caused by acid reflux and consumption of specific foods. Consult with her physician if her dentist cannot find any dental causes.
Tonsils /bad breath. Tonsillar abscess can be a source of fetid odor. An ENT consult would be wise.
Try this. Junior is old enough to manage this. 3x daily flossing of the teeth, running floss across back of tongue is a good start. It takes a large tonsillolith to cause really bad breath; ask your physician or she may try getting it out herself with a mirror, penlight, and perhaps an unwound paper clip. Be careful. Rule out a zenker diverticulum, sleep apnea, reflux, foreign body in nose.