"Enough pieces..." The primary question in Twilight's mind was 'would that work?' Repairing a mirror was easy enough, but using different pieces of different mirrors less so. She could think of ways to do it, but the magical proponent confused it. Theoretically the mirrors all led to one place which would act as a nexus, otherwise Starswirl would've needed a dozen mirrors in each place, so the spell in each mirror shouldn't be an issue because they'd all be the same. But would it still work to combine pieces from several mirrors? Twilight didn't know, and was worried that without an original frame to hold the mirror, it'd be a waste of time to even try. Still, if things got so hopeless that she'd be willing to try it, she might as well have the components she would need.