Help please! Is celiac disease always associated with severe symptoms and malnutrition?

NO. celiac disease can be hidden- or latent- and not associated with severe disease and symptoms or malnutrition. It depends on the individual's immune system and the antibodies it produces in response to gluten. It can be quantified by testing for antibodies and by an endoscopy to look at the degree of intestines that are affected. It can be graded as minimal to severe.
Not always severe. It can sometimes be found incidentally when working up other conditions like osteoporosis or iron deficiency. It always can cause decreased nutrient absorption, but depending on duration and eating habits, it may or may not lead to malnutrition.