I strongly urge you not to go down this road. I don't know if your cousin's claim has any validity, but the Bible is clear: We should avoid anything that might involve us with spiritual or occult forces that are not from God. The Bible warns, "Let no one be found among you ... who practices divination or sorcery" (Deuteronomy 18:10).
Instead, I urge you to seek God's help to deal with your hurt. What does this mean? On one hand, it means avoiding seeking revenge. If the person who hurt you has done wrong, she is ultimately accountable to God for what she's done -- and God will deal with her in His way, and in His time. The Bible says, "Do not take revenge... for it is written: 'It is mine to avenge; I will repay,' says the Lord" (Romans 12:19).
On the other hand, leaving things in God's hands also means seeking His forgiveness for our anger and hatred -- which are sins. They are like an acid eating away at our souls -- and we need to get rid of them. Don't let them destroy you -- because they will, if you allow them to.
How is this possible? It's possible only by turning to God for help, and asking Christ to come into our lives. Seek His forgiveness for your sins, and ask Him to begin changing your life from within. Then ask Him to help you say what Jesus said from the cross: "Father, forgive them, for they do not know what they are doing" (Luke 23:34).