I work as a pool maintenance technician in Texas. There are laws that are pretty strict for public pools for anti-entrapment drains
From what I've been able to read and from what I've read from interviews, the pipe was like 6" wide and didn't have a cover. I believe it was a wall return that she was sucked into. But it was plumbed backwards and so it was pulling water instead of pushing
I work with multiple river pumps and they're frequently the biggest pumps in the pump room. So the water they return is at a pretty high flow rate and none of them have a cover on the pressure side. The ones I work with have multiple openings of an inch or two
But the main reason this happened was someone fucked up with plumbing the pump and used the discharge side for the pressure side. No idea how someone wouldn't notice
I think I read that they didn't disclose that they were renovating and adding a river. No idea why it wasn't looked at either. So, so, so many levels of failure lead to this
Dunno if it changes anything, but user224 posted this link elsewhere in this discussion, and it says the pipe was 30cm (almost a foot) in diameter -- I'm no expert, but the photos in this and OP's article seem to show an opening about that size to me. I only mention it because that seemed uncommonly large to me.