The World Federation One Stop Fiqh

Ruling 436

If a girl who does not know whether she has completed nine years of age experiences bleeding that does not have the attributes of ḥayḍ, it is not ḥayḍ. If it has the attributes of ḥayḍ, then considering it to be ḥayḍ is problematic [i.e. based on obligatory precaution, it must not be considered to be ḥayḍ], unless one is confident that it is ḥayḍ, in which case the girl will be considered to have reached the age of nine.