I have worked with chronic pain patients since 1992, and I am now Board Certified in Psychiatry-- I say this to help deflect the anger that will follow my next sentence...
In my experience, an 8-y-o with 'chronic pain', without a genetic, congenital, or other known abnormality (for example traumatic injury) needs a psychiatric assessment. Chronic pain is usually caused, or at least aggravated, by psychiatric illness when it presents at such a young age. Now that she had had the pain for over ten years we know that it is likely related to psychodynamic factors, as it is virtually impossible for a physical condition to remain hidden for that long.
If nothing else, we know that chronic pain causes depression, and vice versa... so just seeing a mental health professional for support would probably be beneficial.
I can relate to what your kids are going through. I was diagnosed with fibro in January. I have not found any medications that help me either. Even morphine and tramodol don't work. If your daughter is suicidal, has her Dr tried different anti depression meds? Some can increase thoughts of suicide. She should also see a physiatrist. Keep encouraging her, not to give up hope. There will be some good days eventually, just hang in there. To find a good Dr experienced in treating fibro you can check with the arthritis foundation or fibromyalgia association. Best wishes that she will get better soon. "Fibromyalgia The Complete Guide from Medical Experts and Patients" by Sharon Ostalecki is a good book to read. Try to find a support group for her as well.
I know what you must be going thru with your daughter because right now i am going thru the same with my 11 year old child and can not seem to find an answer to his pain and he also is getting very depressed because he can not understand why he is in so much pain from his muscles and bones. good luck I hope you can find an answer soon.