My friend has had her second menstrual period and it's lasted 4 weeks, is there any explanation?

My friend has had her second menstrual period and it's lasted 4 weeks, is there any explanation?
It could be stress or an hormonal unbalance. Tell her to see the doctor if it does not stop soon.
I don't know the explanation but it isn't right. She will become anemic if she isn't already. She needs to see a doctor or ER.