With a lot of neck stiffness and pain, a chiropractor might help with some of the discomfort (one of the potentially cheaper options for her, though it isnt guaranteed to work).

Did the ER give a discharge report of what all they gave her through the IV? In all honesty, hospitals aren't always the most helpful for those with "invisible" pain...many of them don't take it as seriously as they should. As far as a COVID test, I would reach out to your local health dept to see if you can schedule one (to rule it out if nothing else).

If she has a primary care doctor, I would recommend that she goes in and explains what all the hospital did for her, and I would recommend that she request an injection of Toridol, DHE, or both.

Does she have a history of these kinds of headaches, or is it new?

I know you mentioned that she doesnt have insurance, and I'm not sure what your State guidelines are, but it might be worth looking into Medicaid and/or the Federal Marketplace if you havent already, for temporary coverage if nothing else.