Late period?!

Late period?

i know stress can delay your cycle but my girlfriend said shes not stressed and i dont think shes had any sickness what can be wrong?

1) She could be pregnant (not implying anything)
2) Lack of sleep
3) Different living conditions (moving, climate, etc)
4) Exercise
5) Change in diet

Any of these can cause a late period. If it's only late by a few days, don't worry. That's normal. If it's by weeks, then I would be a little concerned. Have her talk to her doctor about it in her next annual visit.