Hello,
For such sudden bald spots, tinea capitis or fungal infection of the scalp needs to be ruled out.
It is contagious and can spread direct contact with someone who has the condition, or if you touch contaminated items such as combs, hats, clothing, or similar surfaces. Diagnosis is by clinical examination of the scalp as well as a skin lesion biopsy with microscopic examination.Anti-fungal medications, taken by mouth, are used to treat the infection.
It is important to keep the area clean. A medicated shampoo, such as one containing selenium sulfide like selsen may also help.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Are there any other symptoms on the skin? If not, I would encourage your girlfriend to visit her physician to make sure all her vitals are okay (ie. blood tests).
Hair loss can also be associated with anorexia. Make sure your girlfriend is eating healthy, balanced meals.