Yeah don't fret over it at all! Periods vary from girl to girl, even when they are related. Some periods are heavy or light - and the symptoms that happening during a period are also as varied! I know I get cramps just before - but am fine during the entire cycle; while my sibling gets cramps and headaches the whole time.
I would only worry if she is starting to miss her period, is bleeding for more than a week, or if the symptoms (especially cramps) last longer than the period itself.