I'm not a doctor but she said she can't eat e.g of pasta because of gluten protein. This may refer she is having celiac disease
Btw, symptoms of this disease can be seen in other disease but if she is a celiac disease this means she has to continue her life with a special diet and special foods. She mustn't eat foods which made of wheat, barley, rye and oats..
This will change her eating habits completely. But on the other hand this way of eating will make her more energetic, more sharp and strong.. She will start to feel better!
If you are interested about this disease you can check research articles and some videos:
Btw, yes Djokovic also follows this gluten free diet..