A psychologist? Oh, brother. The doctors say that when they don't know the answer and they can't admit it, or don't have the tenacity to keep trying. They blame the disease on the patient. If the doctor can't figure it out then it doesn't exist, right?
You know your daughter best. Listen to both your instincts as a mother and your logic. Read old posts in the forum. There were so many people with problems like you are having with finding a diagnosis and finding good doctors.
Excuse me for lingering on this point, but I'm irked on behalf of you and your daughter. What if a car had a huge jarring clanging noise when the engine was running, and the mechanic couldn't figure it out? He'd never say there's no clanking, or that you hear the car clanging because you have a screw loose (pun intended), or that the clanking sound is normal. That would just be ridiculous. Because of course there's a problem. The mechanic would probably say he couldn't figure it out, or he'd call and ask around until he got it fixed. Yes, he'd charge you $400 for the diagnostic, but at least he'd acknowlege the clanging. In this one regard, most doctors are held to a lower standard than a mechanic. Go figure. They can deny what's going on in front of them, heap more worries and problems onto the patient, and call it good. If they were asked if they are doing this, of course they would say no and in their mind, have a perfect explaination of why.
Definitely not all doctors. There are many gems out there who try hard, search every corner, deal honestly with their patients, and don't give up. They stick with it, talk to other doctors and read up to find answers. Or, they say they don't know how to fix it and send you to someone who can. Those doctors are precious when you find one. It's just hard to find one when you don't feel well or are too tired to look.
IMHO... Get a new PCP. And a new neurologist while you are at it. Ask the PCP to check for endocrine and inflammatory diseases at the very least. The first screens for those are just easy blood tests. Has she had MRIs? What did they show? I wouldn't recommend one of these but has she had a lumbar puncture? If so what were the results of that? (no infection?) Make sure your new PCP is an internal medicine doctor, not just a family doctor or run of the mill pediatrician. Consider taking her to a major teaching hospital. Sometimes they are more open-minded, diagnostically creative, and up to date on current research and treatments.
I wish I could wave a magic wand and make everything okay, but I can't. I'm so deeply hoping you find a good doctor and that things get better for her. Please keep us in the loop and let us know how she is doing, okay?
P.S. A psychologist may be a good idea, but for a different reason. More for helping her learn to cope with what's happening to her. Help her stay strong and less afraid. Give her an avenue to talk about it. All good things.