Praise be to Allaah.
Whatever the case, you have to fast once you have reached the age of puberty, which in the case of a girl is when she starts her period, gets pubic hair, experiences erotic dreams or gets pregnant. Having one’s periods is one of the signs of puberty, so you have reached puberty and are accountable, so you have to fast in Ramadaan. In any case, you have to make up the month that you did not fast; you cannot clear yourself except by making up those fasts and repenting, because you were accountable at the time when you did not fast. Your family made a mistake by being too lenient with you. You are not a little child, and you have to repent from this negligence. And Allaah knows best.