Yes revenge.! And the 48 laws of power
Otr, you should apply "Crush your enemy totally"
That is one of the most cruelest principle in the book. Since you wanted revenge on that girl, you should hire some gangsters to splash acid hydrochloric at her face to destroy her beauty completely.
That should do the work for Part I. It will make her lose her self esteem completely that she will be loathing with self hatred, self pity and depression in her life. During that time, you will be laughing out loud as you emerge as the winner seeing her suffering so badly.
To continue on the Part II, you need to be even more ruthless. You hire some gangsters to chop off one of her arms to make her become a handicapped person. This will change her life completely as well and make her become one of the under privilege people in the world who are unfortunate. She will then participate in the local charity fund raising during every time of the year and the people in the public will look at her.
Let's see how she can enjoy this in her life.
Here comes Part III, after completing Part I and II, here is the final part. Hire some kidnappers to kidnap her into another country which is an isolated area and put her in a place that she can seek no help from anyone. She will then rot to her death.
Suffering is better than instant death because instant death wouldn't cause much suffering.
Now I've given you some ideas on how you could take your revenge based on only one law from the fourty eight laws of power. Imagine if you utilize all of the fourty eight laws, what would happen to her?