Brief Answer:
may be due to fluid pressure

Detailed Answer:
Good afternoon. Your description of increasing headache when only bending forward would suggest that there is fluid pressure within the sinus cavities either in the frontal or maxillary areas which are exerting a stretching or pulling force when you flex at the hips or neck.

If you have a fever along with it or thick nasal/mucus discharge of a discolored nature then, this may be more evidence that you are suffering from a secondary headache due to sinus blockage/obstruction and very possibly an infection. Even if there is no fever you may be still suffering from a purulent infection and should have this assessed for possible antibiotic therapy otherwise, things could get complicated not to mention worsening of the headache to where you may start experiencing migraine symptoms.

If your question was adequately responded to could you do me the favor of CLOSING THIS QUERY?

I sincerely hope your daughter can determine what exactly is the matter with her but I would definitely recommend that a brain injury examination be done on her if one was not done when the pedestrian accident occurred.

This query has utilized a total of 10 minutes of professional time in research, review, and synthesis for the purpose of formulating a return statement.

---