Do the fantasies that fall under the name of masturbation count in the vow that the questioner made to herself to abandon masturbation, and does she have to fast days in exchange for breaking this vow?

Deliberately conjuring sexual fantasies may fall under forbidden masturbation, and a Muslim must strive to guard their thoughts. If the questioner was unaware of its prohibition, we hope she does not break her vow and is not obliged to offer expiation; because breaking a vow does not occur with ignorance, according to the Almighty’s saying: "Our Lord, do not take us to task if we forget or make a mistake," and His saying: "And there is no blame upon you for that in which you have erred, but [there is blame for] what your hearts intended." So let her repent to Allah and abandon deliberately conjuring these fantasies.