我有個friend個女今年12.5 years old

岩岩梨月經既日子係唔準確架，要等到月經梨左三年後先會定期。
盡量係月經梨既時候唔好亂食野，可能會影響梨既日子。
梨月經既前後，好容易會受心情所影響而早梨左月經、遲梨左月經及梨月經既時間會長左。

Since she is very young and her menstruation is just appeared (or not long before, such as 1year), her menstruation period is not regular.
If she does not has any sexual behaviour, she will not be pregnancy and it is OK!