How can a girl expiate for having sworn an oath upon herself and her engagement that something specific would happen to her engagement if she were to see a video of a maid torturing a child, and she has indeed seen the video? And will praying two rak'ahs erase this evil supplication?

The Prophet forbade praying against oneself, children, wealth, and servants, fearing that it might coincide with an hour of answered prayers. It is not permissible to pray against oneself to prevent oneself from doing something; rather, one should pray for success and steadfastness. It is advised to turn to Allah and supplicate frequently and insistently, for supplication repels affliction and benefits against what has descended and what has not. Supplicate to Allah with His Beautiful Names and with the supplication of Yunus (peace be upon him). Some scholars have said that a man's prayer against himself out of anger is idle talk for which there is no accountability. As for a vow contingent on something, it must be fulfilled when the contingent condition occurs.