What is the ruling on a girl aged twelve or thirteen who does not fast Ramadan? And is there anything upon her or her family? And should she fast, and if she does not, is there anything upon her?

A woman is obligated to fast if the conditions of obligation are met, which are: Islam, sanity, and puberty. Puberty is attained by menstruation, or the emission of semen with desire (through a wet dream or otherwise), or the growth of coarse hair around the pubes, or reaching fifteen years of age. If these conditions are met, then fasting is obligatory upon her, and she must make up any missed fasts from her period of obligation. If any of these conditions are not met, then she is not obligated.