This sounds a bit like fibromyalgia - I dated someone with that condition for a while and it sounds very similar. It's been described as a constant, low-grade panic attack that spirals and causes more of itself, so all the advice about making her feel safe/relaxed apply. If it is fibro there's a test that can be performed, palpation along certain pressure points feels awful to anyone with fibro.
If it is fibro, there's a weird thing I found in the course of trying to help my partner - a lot of fibro is caused by body toxicity/allergy, particularly heavy metal toxicity. Some people have become symptom-free by detoxification, lemon juice, cilantro, magnesium and chlorella being the main ingredients. Good luck!
