As the droid began rolling at her, Cassie started to slightly panic.  Still, it wasn't the worst thing that could happen.  For one, it made it easier for her to lead it into her acoustic trap, which she started running towards.  Then running the calculations in her head, she started firing her best estimate of the droid's resonant frequency at it.  When it had entered her ring of harmonic amplifiers, she had them all play the same frequency, and though the sound itself could not be heard, its vibrations could be felt as a low rumble to all in the vicinity.  Cassie hoped this would jostle loose something: screws, circuit boards, whatever.  She knew from case files that the omnidroid's greatest enemy was itself, and the concept of applied destructive harmonics was essentially making a material destroy itself from the inside, so she hoped the principle applied here in the same way.  Still if it kept rolling and didn't stay in the trap, damage would be minimal at best.  And Cassie would become a pancake.  She wasn't exactly the most mobile super.