As one feat of which I am aware, she's capable of intercepting, lassoing, and interacting with people explicitly moving at lightspeed. She's not quite as fast as them, but she's fast enough to intercept them and lasso one of them.
She also is fast enough to react-to and block lightspeed energy blasts/bolts/projectiles with her bracers.
'Significant Fraction of Lightspeed' covers it from where I stand. :) Mileage may vary.