My 15 year old is really sick and wont back go to the doctor?

Is she taking antibiotics? Tell her if she runs away she might not get far because her bronchitis could turn into pneumonia and then she'll be admitted to the hospital and might not get out for DAYS. Ask her if she wants that. I have an 18 yr. old and sometimes letting them know these things makes them think twice. I don't know what you've told her but this might help. If you're super worried, you might call someone to talk to her. It's funny how they listen to other people instead of their parents.