Hello,
From the symptoms it looks like some of your mother’s symptoms like weakness, dizzy spells and fainting can be due to adrenal tumors and cause symptoms like headache, palpitations, anxiety attacks, sweating, weight loss, and tremors.
But for pain and diarrhea, possibilities like Crohn’s disease and irritable bowel syndrome need to be ruled out. She needs complete profile of investigations like blood tests, barium follow through, C reactive protein and nuclear scans like white cells scans. However a colonoscopy is the best test for making the diagnosis of Crohn's disease.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
There are dietary supplements on the market which will help your Mother to gain her strength and health which are hypo allergenic. But a Dietitian will be able to help her decide which one she can take and which foods she can digest without upsets. All the best.