You will need her at level 75 for her upgraded Trpl+ buff, which turns into an insane 5t, 3 CD 50% buff. So just buff buff buff. That's her main use. Once Light gets access to Tiaras, that'll be 91% Combo rate from that buff alone.
First ability is a debuff and in a frame that Light was sorely lacking, and you use the third to heal up whenever necessary.