I think the “theme” is more business/day dresses in the King’s graduation photos. The women are mostly wearing shirts or high necked day dresses. I seem to remember there being lots of informal advice about comfort, heels, safety pins, wearing things that the gown can be affixed to, gown sleeve length, trip hazards 😂 etc, as well the official dress code, when my DC graduated. I would guess that is why most have opted for high necklines.
I think it would be fine but your DD might feel a bit over dressed if she doesn’t like to stand out from the crowd. If she doesn’t care and the dress makes her feel great, go for it. On a practical note, I do think the sleeves might make a hump on her shoulders so the gown and hood don’t sit flat though, and the neckline is a bit low for attaching the hood so it might not look great or be uncomfortable.