What is the ruling of Islamic law on one who bound herself to abstain from marriage and children if she failed to adhere to an oath to lose weight, and then broke her oath?

It is absolutely impermissible to invoke curses upon oneself, and one must repent from such acts. Whoever repents with sincere repentance is as if they had not sinned. As for swearing an oath upon oneself, the one who breaks the oath must offer an expiation for an oath: feeding ten poor persons, or clothing them, or fasting for three days if unable to do the former.