I'm not sure I'd rely on that. What's "normal" for her might not be what's normal for average people. Before I got my first pair of glasses, I didn't realize that you could actually see raindrops falling from the sky (at least sometimes). When people would say "Look at it rain!" I could see the ground getting wet and puddles forming and I thought that's all anyone could see. I thought I could see fine and I didn't know I was missing them.
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That is why I said compare it to what the OP could see. Have her DD read something far away that the OP could read easily and see.
I was there only it was me, I never realized I couldn't see far away. I was always in the front row being short and we arranged by grades, so I was never in the back of the room. The only thing I couldn't see was the calendar but I thought no one could!