There is a young lady who has reached the age of 12 or 13 years and the blessed month of Ramaḍān passed her and she did not fast it. Is there anything due on her or her family? Should she fast, and if she does not fast is there any sin on her?
The woman is considered responsible under the following conditions: Islām, sanity and puberty .Puberty is attained by menstruation or a wet dream or the growth of coarse pubic hair around the sexual organ or reaching the age of 15. Therefore, this young lady, if she fulfils all the conditions of responsibility, fasting is obligatory upon her and she must make up for the days that she did not fast during the time of her responsibility. If one of the conditions is not present (Islām, sanity and puberty) then she is not responsible and there is nothing upon her.
Reference: Permanent Committee for Research and Verdicts
Fatawa Islamiyah Page 242 Vol:2