If you have not noticed any signs of 2E, and her visual processing checks out ok, I would be leaning toward thinking that she just "checked out" for that one subtest. All kinds of things can make this happen. She could have been hungry, tired, distracted by something outside or in the room, or she might not have understood the instructions properly. Or she might have thought that that section was stupid or too easy and stopped trying. A test is a snapshot of one moment in time, and there are lots of things that can make us not perform at our best.

A talent search test would be a reasonable and economical next step.