There is a relationship between the 2 in that a lot of people who are in the predicament that many folks around here are in suffer from both to a degree at least.
My 2 cents before others offer vastly different opinions: A anti-Candida diet will not, per se, help adrenal fatigue. My advice is to make sure your mother is eating as healthy as possible. I'd follow most of the Candida diet because it cuts out a lot of crap you should not be eating. But I, personally, draw the line at the pointless elimination of fruit and complex carbs.
The root case of Adrenal Fatigue is not Candida, of course, but you can assume that both of these conditions stem from the same root cause. What are your mother's other symptoms? Does she sleep well? Does she suffer from any digestive problems? I imagine the others symptoms will get you closer to figuring out what she should do than the fact that she has Adrenal Fatigue and Candida. Explicit details about her other symptoms and her digestion might be of more help.