One of my friends has these kind of periods because she has anaemia - iron deficiency. Try taking a blood test just to make sure she has and adequate amount of iron in her blood.
It is not OK. While some young women will have heavy or irregular periods during their first year of periods, these sound really bad - and she is probably pretty anemic by now because of them! Given these periods and her weight, she needs to be checked for a low thyroid level if she hasn't already - that can cause overweight and heavy periods. And if her blood tests are normal it would not be unreasonable for her to go on the pill to regulate her periods and let her have a normal life. I would get her in to see a gynecologist. Best wishes.
I myself have periods like this all the time, even at her age. No one can find a darn thing wrong in my case. I would suggest taking her to a gynecologist as well and they will probably order an ultra sound and put her on the pill which for me didnt work. But I hope you find some reason and help.