All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
We ask Allah, the Exalted, to keep you steadfast on repentance from doing this misdeed and from corrupting your fasting. There is a difference of opinion among the scholars concerning the nullification of a woman’s fast through inserting something into the vagina. Sheikh Al-Islam Ibn Taymiyyah is of the opinion that such an act does not break a woman's fast though she should stay away from it to be on the safe side.
Masturbation does not nullify the fast unless it is accompanied by the ejaculation of semen. Under all circumstances, you are not required to make up for those days even if you were certain that you had ejaculated if you were ignorant of the Sharee'ah ruling. Our Fatwa in this regard is “the ignorant is legally excused and his fasting is not nullified by any of the fasting nullifiers if he was ignorant about its ruling”.
Allah knows best.