How come a 14 year old girl be getting frequent headaches?

Many causes: There are many causes of headaches, including muscle tension (particularly in the neck and shoulders) and eye strain. Perhaps the most common cause of headaches is dehydration; try drinking plenty of water during the day to see if this helps. There are other more serious causes of chronic headaches; best to check in with your doc if this persists.

Depends: There are many reasons why a teenager could be getting headaches. Stress, infection, trauma, family history, eye strain, jaw problems, foods, etc. Also, there are many types of headaches and equally as many ways to treat them. I would recommend that the 14 yo be seen by her primary doctor for an evaluation and if needed, the pcp can refer to a headache specialist.