it's never normal. =)
women are supposed to have their period monthly. if they don't, there must be a hormonal imbalance. In your case, these questions should be asked:
Every month ba jud xa dug-on?
If yes, then there's really something wrong if nilapas na ug 1 month ang delay. A chance of being pregnant is present. If no, then it's probably the same problem with the previous months.
Is she sexually active?
If yes, then there is a big possibility that she may be pregnant. If no, hormonal prob jud cguru na.
Pregnancy Test:
The best way to take it is 10 days after sexual intercourse (if im not mistaken). It's when the woman's HCG levels are high if pregnant mao mu positive na. True, there are times nga ang PT ky negative nia possible nga pregnant and positive pero false alarm di ay.. That's why you should take PT sa sakto nga adlaw.
Menstruation:
There are some pregnant women who still have their menstruation even if they are pregnant. Peru, rare ra kaau ni xa ma happen but it's not impossible. One sign pud if you're pregnant is that magbleeding ka. some may misinterpret it as menstruation. Spotting ra di ay toh. pero naa poi uban nga dili magspotting.
BEST WAY TO KNOW IF PREGNANT OR NOT
take an ultrasound. =D you'll know.