What is the ruling on one who swore to stop listening to music and watching movies, saying: "O Allah, if I do such-and-such, then do such-and-such to me," and she is now regretful and wishes to go back, so does she fear that Allah will do to her what she said?

It is not permissible for a person to invoke evil upon themselves, whether they have committed forbidden acts or not, because the Prophet, peace and blessings be upon him, forbade it, for the prayer might coincide with a time of acceptance. One must abandon forbidden acts out of fear of Allah, and seek His guidance for steadfastness.