Based on how Riker described it, it sounded like it was already broken, and it was phasing in and out, kinda like a flickering light, and stopped “flickering” once it was partially inside of the asteroid, where it finally materialized. This was after Riker and Pressman had left in an escape pod.
Frankly, when I watched this episode when it first aired, it really disturbed me.
Wherever she falls, there shall she be buried… because she is molecularly fused with the floor