My friend says that she has been getting sores/cuts in her mouth but they just appear , what can that be?

Mouth sores: Perhaps they are "canker sores" (aphthous ulcers), which are sometimes associated with citrus acidity or with trauma (from toothbrush or biting cheek). Swishing a mix of mouthwash, warm salt water (1 tsp in tumbler of water), and hydrogen peroxide may help (don't swallow). Orajel/anbesol can numb discomfort. Otc glyoxide also works. If worse, see doc.

Nutritional deficien: This may be associated with vitamin deficiencies caused by dieting, . I would see your md for a nutritional assessment as well comprehensive metabolic profile and possible autoimmune work up.