First, they are wearing 3d suits. There is a huge helmet with a lot of sensors to track the head and the face, they can't put glasses with it on them.

Second, Vivi pushed Pekora, and it seem as if she was expecting to be pushed.
If not she wouldn't have fallen on the ground. She only let herself fall into the ground, because staff put a cushion there before hand.

Third, how they did not see each other before? The whole 3d capturing thing, doesn't allow the 3d room to have curtains or anything.
When pekora was walking, it didn't seem as if there was a staff member helping her to walk. So she was able to see where she was walking.