I was hoping that someone else would answer this for you. But, since they haven't, I'll give it a try.
My daughter, now 20, has experienced intermittent periphial neuropathy since the age of 14. She now has water retention and irritable bowel syndrome. Are these connected?
Probably not. Peripheral Neuropathy can result from a number of conditions. It can be disease, a birth defect, diabetes, even exposure to certain chemicals. That it is intermittent might suggest a pinched nerve somewhere. Your daughter needs to ask lots of questions to determine the exact nature of her illness.
The cause of IBS is not clearly known yet. It's rather like some little thing irritates the bowel and it becomes inflamed. Some medications can cause the water retention also. If her IBS is really bad, there are medications that can give some relief. She might want to see a specialist.
I have found that, during an IBS flare up, if I go on a clear liquid diet for a couple of days followed by a bland diet for a week, that seems to calm it down. It's a tedious balance because the affected has to avoid raw vegetables and fruit, but still eat a balanced diet. If that weren't bad enough, just when you think you've got it beat, it goes the opposite direction and you get severly constipated. IBS isn't just an illness, it's a lifestyle.
She has been tested for diabeties recently and had a Cat Scan of her affected leg at 14 . What tests does she need and what diseases could cause this?