>>1399095The first version of MLP: FiM had 7 main characters. Tracy was one of them. But during development Lauren Faust had to remove one of the seven, due to financial difficulties. She picked Tracy.
Her life ruined, Tracy fell into a deep dark pit of depression. Her entire carrier was ruined. She had to see doctors. After a year of treatment she defeated her depression.
She channeled it into hatred. She swore vengeance to destroy Faust and become a main character on the show, whatever the cost.
This means Tracy has to kill off at least one of the mane 6 to absorb her element.