12 yr old has 1 month prolonged period nonstop?

Hi,
Welcome to ehealthforum.
Prolonged and heavy menstrual period along with presence of abdominal cramps is not normal. Do not ignore her symptoms. Consider visiting her doctor/gynecologist for thorough evaluation to look for the underlying cause for the bleeding. Possibilities of anemia, bleeding disorder, vitamin deficiency, thyroid hormonal abnormalities, other hormonal derangements cannot be ruled out. Treatment as needed (based on examination findings and investigations results) would be started to help her control the bleeding and regulate periods. She should consider being in regular monitoring and follow-up with her treating doctor/gynecologist and report any new/abnormal symptoms immediately. Drink plenty of water. Take adequate rest. Maintain healthy diet and lifestyle.
Take care.