After coming to the music scene after not being able to make her music.
With Grande being one of the biggest stars nowadays she stands in the way of Kesha and could slow down her fame and even stopping her records selling and may result in her disappearance from the music world as a whole.
Kesha was at a bar during the grammys and was seen at some points looking out , looking very suspicious,  maybe she was looking for someone. She was accused of playing the elevator game.
She may of killed Grande to get to the top of the charts and take her career back.