Hi! Your mother seems to be suffering from gluten sensitive enteropathy
which is a chronic inflammatory disease of the small intestine
which is triggered by a delayed onset allergic reaction
to gluten in the normal diet.It is also accompanied by an intensely itchy rash .The only effective treatment is strict life-long and complete avoidance of wheat, rye and barley.Rather such patients can eat maize and rice.As colonoscopy
is normal so nothing serious.Making these dietary changes shall help!