What can influence the degree of menstrual bleeding?

My sister is 19, she has regular periods but has the bleeding for only a three days. Is that healthy or any improper ? I want to know what elements do regulate the menstrual bleeding in women?? (Experts' opinions are more favored). Is that possible and healthy to regulate the bleeding as per our wish? I want to mainly know "WHAT HIGHLY REGULATES THE MENSTRUAL BLEEDING".. (NO LINKS PLEASE) Thanks :-)