My daughter has periods for 5 years,mostly regular.this month she's 12 days late.i am worried.she still didn't have sexual relationship.likely causes?

It happens sometimes: In a person with regular periods, some causes of a late period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (like birth control pills), hormonal imbalances, etc… Seeing a doctor is a good idea if symptoms are persistent, recurring, or worrisome. (Pregnancy is the common cause of a missed period, if sexually active.)