I have suffered with fibro for years. Fortunately headaches like you describe have not been a problem for me. I agree with getting her tested for Lyme disease. As Nicole said, they have many symptoms in common. Many people who have Lyme have been misdiagnosed with fibro.
From what I know of the two, I think I would rather have the fibromyalgia, though it is a terrible condition to live with too. I have taken many medications and combinations of medicines to finally keep mine somewhat controlled. That can take years. A good rheumatologist can be a big help. We are all different in symptoms and meds, so what works for one of us, doesn't necessarily work for someone else.
I wish her luck and pain free days.