Lara's eyes were basically scarlet at this time, and her hand lit up with flames of a purple color. She seemed like she was going to attack Dante in his moment of weakness, but despite her posture, she never actually made a move.
It was not from fear, but because of the spectators looking on. It was not conducive to her plans for her reputation to be any more negative than it already is. The killing of the students she could easily justify given what they had done, Dante had already recorded and uploaded enough evidence to the Central AI for the school.
That was what even brought her out here so quickly. Partly because Dante had grown so powerful so quickly and partly because she needed to be the one to resolve the situation, not Dante.